Polytetrafluoroethylene powder, binder for electrode, electrode mixture, electrode, and secondary battery

Abstract

To provide polytetrafluoroethylene powder for a binder for an electrode, a binder for an electrode, an electrode mixture, an electrode, and a secondary battery that are sustainable products and able to suppress the gas generation inside a battery cell and deterioration of battery characteristics.SOLUTION: Polytetrafluoroethylene powder used for a binder for an electrode substantially excludes moisture and a fluorine-containing compound with a molecular weight of 1000 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to polytetrafluoroethylene powder, electrode binders, electrode mixtures, electrodes, and secondary batteries. [Background technology]

[0002] Secondary batteries, such as lithium-ion batteries, are used in small, portable electrical and electronic devices such as notebook computers, mobile phones, smartphones, tablet computers, and ultrabooks, due to their high voltage, high energy density, low self-discharge, low memory effect, and the possibility of ultra-lightweight design. Furthermore, they are being put into practical use as a wide range of power sources, from on-board power supplies for automobiles to large-scale stationary power supplies. There is a demand for even higher energy density in secondary batteries, and further improvements in battery characteristics are required.

[0003] Patent Document 1 describes an energy storage device in which at least one of the cathode and anode contains a polytetrafluoroethylene mixed binder material.

[0004] Patent documents 2 and 3 describe the use of an aqueous dispersion of polytetrafluoroethylene as a binder for batteries. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Special Publication No. 2017-517862 [Patent Document 2] Japanese Patent Publication No. 2004-31179 [Patent Document 3] Japanese Patent Application Publication No. 11-343317 [Overview of the project] [Problems that the invention aims to solve]

[0006] This disclosure aims to provide polytetrafluoroethylene powder for electrode binders, electrode binders, electrode mixtures, electrodes, and secondary batteries that are sustainable products and can suppress gas generation inside battery cells and degradation of battery characteristics. [Means for solving the problem]

[0007] This disclosure (1) provides a polytetrafluoroethylene powder for use as an electrode binder, which is substantially free of water and fluorine-containing compounds with a molecular weight of 1000 or less.

[0008] The present disclosure (2) also provides an electrode binder consisting substantially of polytetrafluoroethylene powder, wherein the polytetrafluoroethylene powder substantially does not contain water and fluorine-containing compounds with a molecular weight of 1000 or less.

[0009] Disclosure (3) is an electrode binder according to Disclosure (2) wherein the polytetrafluoroethylene powder substantially does not contain any of the fluorine-containing compounds represented by the following formulas. F(CF2)7COOM, F(CF2)5COOM, H(CF2)6COOM, H(CF2)7COOM, CF3O(CF2)3OCHFCF2COOM, C3F7OCF(CF3)CF2OCF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2OCF2CF2OCF2COOM, C2F5OCF(CF3)CF2OCF(CF3)COOM, CF3OCF(CF3)CF2OCF(CF3)COOM, CF2ClCF2CF2OCF(CF3)CF2OCF2COOM, CF2ClCF2CF2OCF2CF(CF3)OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM, and, [ka] (In each formula, M is H, metal atom, NR 1 4. Imidazolium, pyridinium, or phosphonium, which may have substituents. 1 (This is either H or an organic group.)

[0010] Disclosure (4) is an electrode binder according to Disclosure (2) or (3), wherein the content of the fluorine-containing compound is less than 25 ppb by mass relative to the polytetrafluoroethylene powder.

[0011] Disclosure (5) is an electrode binder in any combination of the polytetrafluoroethylene described above with any of Disclosures (2) to (4), which include tetrafluoroethylene units and modified monomer units based on modified monomers copolymerizable with tetrafluoroethylene.

[0012] Disclosure (6) is an electrode binder according to Disclosure (5), wherein the modified monomer is at least one selected from the group consisting of perfluoro(methyl vinyl ether) and hexafluoropropylene.

[0013] Disclosure (7) also provides an electrode mixture comprising an electrode binder of polytetrafluoroethylene powder according to Disclosure (1) or any combination thereof with any of Disclosures (2) to (6), and an electrode active material.

[0014] Disclosure (8) also provides an electrode comprising an electrode binder of polytetrafluoroethylene powder according to Disclosure (1) or any combination thereof with any of Disclosures (2) to (6), an electrode active material, and a current collector.

[0015] The present disclosure (9) also provides a secondary battery comprising the electrodes of the present disclosure (8). [Effects of the Invention]

[0016] According to this disclosure, it is possible to provide polytetrafluoroethylene powder for electrode binders, electrode binders, electrode mixtures, electrodes, and secondary batteries that are sustainable products and can suppress gas generation inside battery cells and degradation of battery characteristics. [Modes for carrying out the invention]

[0017] In recent years, as part of sustainable chemical management, there has been a growing need to reduce the emission of low-molecular-weight fluorine-containing compounds, including PFOA. Furthermore, there is a need to suppress gas generation within battery cells and the degradation of battery characteristics caused by moisture and impurities in electrode binders. Through diligent research, it was discovered that PTFE powder with reduced moisture and specific impurities can be obtained by processing under extremely limited conditions, and that this PTFE powder can be suitably used as an electrode binder.

[0018] The following provides a detailed explanation of this disclosure.

[0019] This disclosure provides a polytetrafluoroethylene (PTFE) powder for use as an electrode binder, which is substantially free of water and fluorine-containing compounds with a molecular weight of 1000 or less. Since the PTFE powder of this disclosure has the above-described structure, it can provide a sustainable product as a binder material for electrodes. Furthermore, when used as an electrode binder, it can suppress gas generation inside the battery cell and deterioration of battery characteristics (e.g., decrease in capacity during high-temperature storage), and can also improve electrode strength. In addition, since it can be mixed with electrode active material as a powder, there is no need to use organic solvents, which reduces the process and costs associated with the use of organic solvents.

[0020] The PTFE powder of this disclosure is substantially free of moisture. This suppresses gas generation and degradation of battery characteristics, and also improves electrode strength. Furthermore, it is advantageous in the production process because it allows for a wide selection of electrode active materials to be combined with it. Substantially free of moisture means that the moisture content of the PTFE powder is 0.010% by mass or less. The above moisture content is preferably 0.005% by mass or less, more preferably 0.003% by mass or less, even more preferably 0.002% by mass or less, and particularly preferably 0.001% by mass or less. The above moisture content is measured by the following method. The mass of PTFE powder is measured before and after heating at 150°C for 2 hours, and the mass is calculated according to the following formula. Three samples are taken, and the calculation is performed for each sample. The average value is then used. Moisture content (mass %) = [(Mass of PTFE powder before heating (g)) - (Mass of PTFE powder after heating (g))] / (Mass of PTFE powder before heating (g)) × 100

[0021] The PTFE powder of this disclosure is substantially free of fluorine-containing compounds with a molecular weight of 1000 or less. "Substantially free of fluorine-containing compounds" means that the amount of fluorine-containing compounds is 25 ppb by mass or less relative to the PTFE powder. The amount of the fluorine-containing compound is preferably less than 25 ppb by mass, more preferably 10 ppb by mass or less, even more preferably 5 ppb by mass or less, particularly preferably 3 ppb by mass or less, and especially preferably 1 ppb by mass or less. The lower limit is not particularly limited and may be an amount below the detection limit.

[0022] The amount of the above-mentioned fluorine-containing compound with a molecular weight of 1000 or less is measured by the following method. Weigh 1 g of the sample, add 10 g (12.6 ml) of methanol, and sonicate for 60 minutes to obtain an extract. Concentrate the obtained extract by nitrogen purging as appropriate, and measure the fluorine-containing compounds in the concentrated extract by LC / MS / MS. Extract molecular weight information from the obtained LC / MS spectrum and confirm its agreement with the structural formula of the candidate fluorine-containing compound. Prepare aqueous solutions with five or more levels of the standard substance, perform LC / MS analysis of each aqueous solution, plot the relationship between the content and the area area corresponding to that content, and draw a calibration curve. Using the above calibration curve, convert the area area of ​​the LC / MS chromatogram of the fluorine-containing compound in the extract to the content of the fluorine-containing compound. The detection limit for this measurement method is 10 mass ppb.

[0023] The amount of fluorine-containing compounds with a molecular weight of 1000 or less can also be measured by the following method. Weigh 1 g of the sample, add 10 g (12.6 ml) of methanol, sonicate at 60°C for 2 hours, and after standing at room temperature, remove the solids to obtain the extract. Concentrate the obtained extract by nitrogen purging as appropriate, and measure the fluorine-containing compounds in the concentrated extract by LC / MS / MS. Extract molecular weight information from the obtained LC / MS spectrum and confirm its agreement with the structural formula of the candidate fluorine-containing compound. Prepare five levels of methanol standard solutions of fluorine-containing compounds with known concentrations and measure them using a liquid chromatograph-mass spectrometer. For each concentration range, create a calibration curve using a first-order approximation from the methanol standard solution concentration and the integral value of the peak. From the above calibration curve, measure the content of fluorine-containing compounds in the extract and convert it to the content of fluorine-containing compounds in the sample. The detection limit for this measurement method is 1 mass ppb.

[0024] Examples of fluorine-containing compounds with a molecular weight of 1000 or less include fluorine-containing compounds having hydrophilic groups with a molecular weight of 1000 g / mol or less. The molecular weight of the above fluorine-containing compound is preferably 800 or less, and more preferably 500 or less. In the polymer particles obtained by polymerization carried out in the presence of a fluorine-containing surfactant, in addition to PTFE, it is normal for the fluorine-containing surfactant to be included. In this specification, the fluorine-containing surfactant is the one used during polymerization. The fluorine-containing compound having a molecular weight of 1000 or less may be a compound that is not added during polymerization, for example, a compound that is by-produced during the polymerization process. In addition, when the fluorine-containing compound having a molecular weight of 1000 or less contains an anionic part and a cationic part, it means a fluorine-containing compound in which the molecular weight of the anionic part is 1000 or less. It is assumed that PTFE is not included in the fluorine-containing compound having a molecular weight of 1000 or less.

[0025] Examples of the hydrophilic group may be, for example, -COOM, -SO2M, or -SO3M, and -COOM, -SO3M (in each formula, M is H, a metal atom, NR 1 4, an imidazolium that may have a substituent, a pyridinium that may have a substituent, or a phosphonium that may have a substituent, and R 1 is H or an organic group.). Examples of such anionic groups are given.

[0026] As the fluorine-containing surfactant, a surfactant containing fluorine with a molecular weight of 1000 or less in the anionic part (anionic fluorine-containing surfactant) can also be used. The above-mentioned "anionic part" means the part excluding the cation of the fluorine-containing surfactant. For example, in the case of F(CF2) n1 COOM, it is the part of "F(CF2) n1 COO". As the above-mentioned anionic fluorine-containing surfactant, the following general formula (N 0 ): X n0 -Rf n0 -Y 0 (N 0 ) (In the formula, X n0 is H, Cl or and F. Rf n0This is an alkylene group having 3 to 20 carbon atoms, being linear, branched, or cyclic, in which some or all of the hydrogen atoms are substituted with fluorine, and the alkylene group may contain one or more ether bonds, and some of the hydrogen atoms may be substituted with chlorine. 0 The group is an anionic group. Examples of compounds represented by ) are shown. Y 0 The anionic group may be -COOM, -SO2M, or -SO3M. M is H, a metal atom, NR 1 4. Imidazolium which may have substituents, pyridinium which may have substituents, or phosphonium which may have substituents, 1 is either H or an organic group. Examples of the above-mentioned metal atoms include alkali metals (Group 1) and alkaline earth metals (Group 2), such as Na, K, or Li. R 1 For example, H or C 1-10 The organic group may be H or C 1-4 The organic group may be H or C 1-4 It may be an alkyl group. M is H, a metal atom, or NR 1 It may be 4, and may be H, alkali metals (Group 1), alkaline earth metals (Group 2), or NR 1 It may be 4, and may be H, Na, K, Li, or NH4. The above Rf n0 It is acceptable if 50% or more of the H atoms are replaced with fluorine.

[0027] The fluorine-containing surfactant described above may be a single fluorine-containing surfactant or a mixture containing two or more fluorine-containing surfactants.

[0028] Examples of the fluorine-containing surfactants mentioned above include compounds represented by the following formula. The fluorine-containing surfactant may be a mixture of these compounds. F(CF2)7COOM, F(CF2)5COOM, H(CF2)6COOM, H(CF2)7COOM, CF3O(CF2)3OCHFCF2COOM, C3F7OCF(CF3)CF2OCF(CF3)COOM, CF3CF2CF2OCF(CF3)COOM, CF3CF2OCF2CF2OCF2COOM, C2F5OCF(CF3)CF2OCF(CF3)COOM, CF3OCF(CF3)CF2OCF(CF3)COOM, CF2ClCF2CF2OCF(CF3)CF2OCF2COOM, CF2ClCF2CF2OCF2CF(CF3)OCF2COOM, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOM, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOM, and, [ka] (In each formula, M is H, metal atom, NR 1 4. Imidazolium, pyridinium, or phosphonium, which may have substituents. 1 (This is either H or an organic group.) The PTFE powder of this disclosure preferably contains substantially none of the fluorine-containing compounds represented by the above formula.

[0029] In each of the above formulas, M is H, a metal atom, or NR 1 It may be 4, and may be H, alkali metals (Group 1), alkaline earth metals (Group 2), or NR 1 It may be 4, and may be H, Na, K, Li, or NH4. R 1 H or C 1-10 The organic group may be H or C 1-4 The organic group may be H or C 1-4 It may be an alkyl group.

[0030] If the PTFE powder of this disclosure substantially does not contain any of the fluorine-containing compounds represented by the above formula, gas generation and degradation of battery characteristics can be further suppressed, and electrode strength can be further improved. "Substantially free of any of the fluorine-containing compounds represented by the above formula" means that the amount of such fluorine-containing compound is 25 ppb by mass or less relative to the PTFE powder. The amount of the fluorine-containing compound is preferably less than 25 ppb by mass, more preferably 10 ppb by mass or less, even more preferably 5 ppb by mass or less, particularly preferably 3 ppb by mass or less, and especially preferably 1 ppb by mass or less. The lower limit is not particularly limited and may be an amount below the detection limit.

[0031] The PTFE powder disclosed herein has the following general formula: [C n-1 F 2n-1 COO - ]M + (In the formula, n is an integer from 9 to 14, preferably an integer from 9 to 12, M + ∫ represents a cation. It is also preferable that the fluorine-containing compound represented by ∫ is substantially free of ∫. This can further suppress gas generation and degradation of battery characteristics, and can also further improve electrode strength. The cation M in the above formula + The M that constitutes this is the same as the M described above. "Substantially free of the fluorine-containing compound represented by the above formula" means that the amount of the fluorine-containing compound is 25 ppb by mass or less relative to the PTFE powder. The amount of the fluorine-containing compound is preferably less than 25 ppb by mass, more preferably 10 ppb by mass or less, even more preferably 5 ppb by mass or less, particularly preferably 3 ppb by mass or less, and especially preferably 1 ppb by mass or less. The lower limit is not particularly limited and may be an amount below the detection limit.

[0032] The PTFE powder of this disclosure preferably has a standard specific gravity (SSG) of 2.200 or less, more preferably 2.180 or less, even more preferably 2.170 or less, even more preferably 2.160 or less, even more preferably 2.150 or less, especially preferably 2.145 or less, and particularly preferably 2.140 or less, in terms of being able to further suppress gas generation and deterioration of battery characteristics, and improving binding strength, electrode strength, and electrode flexibility. The above SSG is also preferably 2.130 or higher. The above SSG is measured using a sample molded in accordance with ASTM D 4895 and measured by the water displacement method in accordance with ASTM D 792.

[0033] The PTFE powder of this disclosure preferably has a high molecular weight, and in terms of improving binding strength and electrode flexibility, the average primary particle diameter is preferably 350 nm or less, more preferably 330 nm or less, even more preferably 320 nm or less, even more preferably 300 nm or less, especially preferably 280 nm or less, particularly preferably 250 nm or less, and also preferably 100 nm or more, more preferably 150 nm or more, even more preferably 170 nm or more, and particularly preferably 200 nm or more. The above average primary particle diameter is measured by the following method. A PTFE aqueous dispersion is diluted with water until the solid content concentration reaches 0.15% by mass. A calibration curve is created by measuring the transmittance of 550 nm projected light per unit length of the resulting diluted latex and the number-referenced length-average particle diameter determined by measuring the direction using transmission electron microscopy. Using this calibration curve, the number-average particle diameter is determined from the measured transmittance of 550 nm projected light for each sample and is defined as the average primary particle diameter.

[0034] The PTFE powder of this disclosure may have an average secondary particle diameter of 350 μm or more, preferably 400 μm or more, more preferably 450 μm or more, even more preferably 500 μm or more, especially preferably 550 μm or more, particularly preferably 600 μm or more, and also preferably 1000 μm or less, more preferably 900 μm or less, even more preferably 800 μm or less, and even more preferably 700 μm or less. The above average secondary particle diameter is measured in accordance with JIS K 6891.

[0035] The PTFE powder of this disclosure is preferably extruded at a reduction ratio (RR) of 100 of 10 MPa or higher, more preferably 12 MPa or higher, even more preferably 15 MPa or higher, even more preferably 16 MPa or higher, and particularly preferably 17 MPa or higher, in that it can further suppress gas generation and degradation of battery characteristics, and improve binding strength, electrode strength, and electrode flexibility. The extrusion pressure in RR100 is preferably 50 MPa or less, more preferably 40 MPa or less, even more preferably 35 MPa or less, even more preferably 30 MPa or less, even more preferably 25 MPa or less, even more preferably 21 MPa or less, and particularly preferably 20 MPa or less, in terms of improving processability.

[0036] The PTFE powder of this disclosure is preferably extruded at 18 MPa or higher in RR300, more preferably at 23 MPa or higher, even more preferably at 25 MPa or higher, even more preferably at 28 MPa or higher, even more preferably at 30 MPa or higher, and particularly preferably at 32 MPa or higher, in terms of further suppressing gas generation and degradation of battery characteristics, and improving binding strength, electrode strength, and electrode flexibility. In RR300, the extrusion pressure is preferably 45 MPa or less, and more preferably 40 MPa or less, in terms of improving processability.

[0037] The extrusion pressure in RR100 is measured by the following method. Mix 50g of PTFE powder and 10.25g of hydrocarbon oil (product name: Isopar E, manufactured by ExxonMobil) as an extrusion aid in a polyethylene container for 3 minutes. At room temperature (25±2℃), fill the extruder cylinder with the mixture and apply a load of 0.47 MPa to the piston inserted into the cylinder and hold for 1 minute. Next, extrude through the orifice at a ram speed of 18 mm / min. The ratio of the cylinder's cross-sectional area to the orifice's cross-sectional area (reduction ratio) is 100. In the latter half of the extrusion operation, the extrusion pressure (MPa) is defined as the load (N) when the pressure reaches equilibrium, divided by the cylinder's cross-sectional area.

[0038] The extrusion pressure in RR300 is measured by the following method. Mix 50g of PTFE powder and 11.00g of hydrocarbon oil (product name: Isopar E, manufactured by ExxonMobil) as an extrusion aid in a polyethylene container for 3 minutes. At room temperature (25±2℃), fill the extruder cylinder with the mixture and apply a load of 0.47 MPa to the piston inserted into the cylinder and hold for 1 minute. Next, extrude through the orifice at a ram speed of 18 mm / min. The ratio of the cylinder's cross-sectional area to the orifice's cross-sectional area (reduction ratio) is 300. In the latter half of the extrusion operation, the extrusion pressure (MPa) is defined as the load (N) when the pressure reaches equilibrium, divided by the cylinder's cross-sectional area.

[0039] The PTFE powder of this disclosure is preferably stretchable, as this further suppresses gas generation and degradation of battery characteristics, and improves binding strength, electrode strength, and electrode flexibility. "Stretchable" means that an stretched material can be obtained in the following stretching tests. The bead obtained by paste extrusion using RR100 as described above is dried at 230°C for 30 minutes to remove the lubricant. After drying, the bead is cut to an appropriate length and placed in a furnace heated to 300°C, where it is stretched at a stretching speed of 100% / second.

[0040] The PTFE powder of this disclosure is preferably stretchable up to 25 times, as this further suppresses gas generation and degradation of battery characteristics, and further improves binding strength, electrode strength, and electrode flexibility. Whether or not it can be stretched 25 times can be confirmed by the following stretching test. The bead obtained by paste extrusion using RR100 as described above is dried at 230°C for 30 minutes to remove the lubricant. After drying, the bead is cut to an appropriate length and placed in a furnace heated to 300°C. Inside the furnace, it is stretched at a stretching speed of 100% / second until it reaches 25 times the length of the bead before the stretching test. If it does not break during stretching, it is determined that it can be stretched 25 times.

[0041] The PTFE powder of this disclosure has excellent handling properties, and its average aspect ratio may be 2.0 or less, preferably 1.8 or less, more preferably 1.7 or less, even more preferably 1.6 or less, even more preferably 1.5 or less, even more preferably 1.4 or less, especially preferably 1.3 or less, particularly preferably 1.2 or less, and most preferably 1.1 or less. The above average aspect ratio may also be 1.0 or more. The above average aspect ratio is determined by observing PTFE powder or a PTFE aqueous dispersion diluted to a solid content concentration of approximately 1% by mass using a scanning electron microscope (SEM), processing images of 200 or more randomly selected particles, and calculating the average ratio of the major axis to the minor axis.

[0042] The PTFE powder of this disclosure preferably has an apparent density of 0.40 g / ml or more, more preferably 0.43 g / ml or more, even more preferably 0.45 g / ml or more, even more preferably 0.48 g / ml or more, and particularly preferably 0.50 g / ml or more, in terms of excellent handling properties. The upper limit is not particularly limited, but it may be as high as 0.70 g / ml. The apparent density mentioned above is measured in accordance with JIS K 6892.

[0043] The PTFE powder of this disclosure preferably has non-melt secondary processability. Non-melt secondary processability refers to the property that the melt flow rate cannot be measured at a temperature higher than the melting point, in accordance with ASTM D-1238 and D-2116, or in other words, the property that does not easily flow even in the melting temperature range.

[0044] The above PTFE may be a homopolymer of tetrafluoroethylene (TFE), or it may be a modified PTFE containing polymerization units based on TFE (TFE units) and polymerization units based on modified monomers (hereinafter also referred to as "modified monomer units"). The above modified PTFE may contain 99.0% by mass or more of TFE units and 1.0% by mass or less of modified monomer units. Furthermore, the above modified PTFE may consist only of TFE units and modified monomer units. Of the above PTFE, modified PTFE is preferred because it can further suppress gas generation and degradation of battery characteristics, and improves binding strength, electrode strength, and electrode flexibility.

[0045] The above-mentioned modified PTFE is preferably such that the content of modified monomer units is in the range of 0.00001 to 1.0 mass% relative to the total polymerization units, in order to further suppress gas generation and deterioration of battery characteristics, and to improve stretchability, bonding strength, electrode strength, and electrode flexibility. The lower limit of the content of modified monomer units is more preferably 0.0001 mass%, even more preferably 0.001 mass%, even more preferably 0.005 mass%, and especially preferably 0.010 mass%. The upper limit of the content of modified monomer units is preferably 0.90 mass%, more preferably 0.80 mass%, more preferably 0.50 mass%, even more preferably 0.40 mass%, even more preferably 0.30 mass%, even more preferably 0.20 mass%, especially preferably 0.15 mass%, even more preferably 0.10 mass%, even more preferably 0.08 mass%, especially preferably 0.05 mass%, and most preferably 0.03 mass%. In this specification, the above-mentioned modified monomer unit means a part of the molecular structure of PTFE that is derived from the modified monomer.

[0046] The content of each polymerization unit mentioned above can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0047] The above-mentioned modified monomers are not particularly limited as long as they can copolymerize with TFE, and include, for example, perfluoroolefins such as hexafluoropropylene [HFP]; hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride [VDF]; perhaloolefins such as chlorotrifluoroethylene; perfluorovinyl ethers; perfluoroallyl ethers; (perfluoroalkyl)ethylene, ethylene, etc. Furthermore, one or more modified monomers may be used.

[0048] The perfluorovinyl ether mentioned above is not particularly limited, for example, the following general formula (A): CF2 = CF - ORf (A) Examples include perfluorounsaturated compounds represented by the formula (wherein Rf represents a perfluoroorganic group). In this specification, the term "perfluoroorganic group" means an organic group in which all hydrogen atoms bonded to a carbon atom are replaced with fluorine atoms. The perfluoroorganic group may have an ether oxygen.

[0049] Examples of the perfluorovinyl ethers mentioned above include perfluoro(alkyl vinyl ether) [PAVE] in which Rf in the general formula (A) above is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5.

[0050] Examples of perfluoroalkyl groups in the above-mentioned PAVE include perfluoromethyl, perfluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl, and perfluorohexyl groups.

[0051] The above perfluorovinyl ethers are further defined as those in the above general formula (A) where Rf is a perfluoro(alkoxyalkyl) group having 4 to 9 carbon atoms, and where Rf is defined by the following formula:

[0052] [ka]

[0053] (In the formula, m represents an integer from 0 to 4.) The base is represented by the following formula, where Rf is:

[0054] [ka]

[0055] Examples include the base represented by (wherein n represents an integer from 1 to 4).

[0056] (Perfluoroalkyl)ethylene (PFAE) is not particularly limited and examples include (perfluorobutyl)ethylene (PFBE), (perfluorohexyl)ethylene, etc.

[0057] Examples of perfluoroallyl ethers include general formula (B): CF2 = CF - CF2 - ORf 1 (B) (In the formula, Rf 1 ) represents a perfluoroorganic group. Examples include fluoromonomers represented by ).

[0058] The above Rf 1The perfluoroallyl ether is preferably a perfluoroalkyl group having 1 to 10 carbon atoms or a perfluoroalkoxyalkyl group having 1 to 10 carbon atoms. The perfluoroallyl ether is preferably at least one selected from the group consisting of CF2=CF-CF2-O-CF3, CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9, more preferably at least one selected from the group consisting of CF2=CF-CF2-O-C2F5, CF2=CF-CF2-O-C3F7, and CF2=CF-CF2-O-C4F9, and even more preferably CF2=CF-CF2-O-CF2CF2CF3.

[0059] As the above-mentioned modified monomer, at least one selected from the group consisting of PAVE and HFP is preferred, and at least one selected from the group consisting of perfluoro(methyl vinyl ether) (PMVE) and HFP is more preferred, in terms of improving stretchability, binding strength, and electrode flexibility.

[0060] As for the other modified monomers mentioned above, at least one selected from the group consisting of VDF, HFP, CTFE, and PAVE is preferred, and at least one selected from the group consisting of VDF, HFP, and CTFE is more preferred, in that it can form an electrode mixture sheet with even greater strength. In terms of improving heat resistance, one preferred embodiment is that the PTFE contains TFE units, VDF units, and HFP units, and the total amount of VDF units and HFP units is 1.0% by mass or less relative to the total polymerization units.

[0061] The above-mentioned PTFE may have a core-shell structure. Examples of PTFE having a core-shell structure include modified PTFE, which contains a core of high molecular weight PTFE and a shell of lower molecular weight PTFE or modified PTFE in the particle. Examples of such modified PTFE include the PTFE described in Japanese Patent Publication No. 2005-527652.

[0062] The above PTFE is preferably such that its endothermic peak temperature is 320°C or higher, more preferably 325°C or higher, even more preferably 330°C or higher, even more preferably 335°C or higher, even more preferably 340°C or higher, even more preferably 342°C or higher, and particularly preferably 344°C or higher, in order to form an electrode mixture sheet with even greater strength. The above endothermic peak temperature is also preferably 350°C or lower. The above endothermic peak temperature corresponds to the temperature at which the minimum point in the heat of fusion curve is obtained by differential scanning calorimetry (DSC) at a heating rate of 10°C / min for fluororesin that has not been heated to temperatures above 300°C. If there are two or more minimum points in a single melting peak, each is considered an endothermic peak temperature.

[0063] Preferably, when the above-mentioned PTFE is heated at a rate of 10°C / min using a differential scanning calorimeter (DSC), one or more endothermic peaks appear in the range of 333 to 347°C in the heat of fusion curve, and the heat of fusion at 290 to 350°C calculated from the above-mentioned heat of fusion curve is 62 mJ / mg or more.

[0064] The above PTFE can form an electrode mixture sheet with even greater strength, and has a number-average molecular weight (Mn) of 3.0 × 10⁻⁶. 6 It is preferable that the above is true, 3.2 × 10 6 More preferably, 3.5 × 10 6 More preferably, the above is true, 3.7 × 10 6 It is even more preferable that the above is 4.0 × 10 6 It is particularly preferable that the above values ​​are met. The above number-average molecular weight is also 7.0 × 10⁻⁶. 6 Preferably, it is 6.5 × 10 6 It is more preferable that the following conditions apply: 6.0 × 10 6 It is even more preferable that the following conditions apply: 5.5 × 10 6 It is even more preferable that the following conditions apply: 5.0 × 10 6 The following is particularly preferable: The above number-average molecular weight is determined from the heat of crystallization estimated by measuring the cooling temperature using a differential scanning calorimeter (DSC) after melting the fluororesin, according to the method described in the following literature. Five measurements were taken, and the average of the three values ​​excluding the maximum and minimum values ​​was adopted. Literature: Suwa, T.; Takehisa, M.; Machi, S., J. Appl. Polym. Sci. vol. 17, pp. 3253 (1973).

[0065] The PTFE powder of this disclosure can be suitably produced by a manufacturing method comprising, for example, the steps of: (A) preparing an aqueous dispersion of PTFE; (B) coagulating the aqueous dispersion to obtain wet PTFE powder; and (C) placing the wet powder in a container with a permeable bottom and / or sides, and heat-treating it at a temperature of 150 to 300°C for 2 hours or more to obtain PTFE powder.

[0066] The aqueous dispersion in step (A) can be produced, for example, by emulsion polymerization.

[0067] The above emulsion polymerization can be carried out by known methods. For example, by carrying out emulsion polymerization of monomers necessary to constitute the PTFE in an aqueous medium in the presence of an anionic fluorine-containing surfactant and a polymerization initiator, an aqueous dispersion containing the PTFE particles (primary particles) can be obtained. In the above emulsion polymerization, chain transfer agents, buffers, pH adjusters, stabilizing aids, dispersion stabilizers, radical scavengers, etc. may be used as needed.

[0068] The aqueous dispersion described above may contain at least one of the fluorine-containing compounds mentioned above.

[0069] Step (A) described above may be a step of emulsion polymerization of TFE and, if necessary, a modified monomer.

[0070] The above emulsion polymerization can be carried out, for example, in an aqueous medium in the presence of an anionic fluorine-containing surfactant and a polymerization initiator. The above emulsion polymerization can be carried out by charging an aqueous medium, the above anionic fluorine-containing surfactant, monomers, and other additives as needed into a polymerization reactor, stirring the contents of the reactor, maintaining the reactor at a predetermined polymerization temperature, and then adding a predetermined amount of polymerization initiator to start the polymerization reaction. After the start of the polymerization reaction, monomers, polymerization initiators, chain transfer agents, and the above surfactants may be added as needed.

[0071] The polymerization initiator described above is not particularly limited as long as it can generate radicals within the polymerization temperature range, and known oil-soluble and / or water-soluble polymerization initiators can be used. Furthermore, polymerization can also be initiated as a redox by combining it with a reducing agent or the like. The concentration of the polymerization initiator described above is appropriately determined depending on the type of monomer, the molecular weight of the target PTFE, and the reaction rate.

[0072] As the polymerization initiator mentioned above, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

[0073] The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, such as dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and disec-butyl peroxydicarbonate, peroxyesters such as t-butyl peroxyisobutyrate and t-butyl peroxypivalate, and dialkyl peroxides such as dit-butyl peroxide. Also, di(ω-hydro-dodecafluoroheptanoyl) peroxide, di(ω-hydro-tetradecafluoroheptanoyl) peroxide, di(ω-hydro-hexadecafluorononanoyl) peroxide, di(perfluorobutyryl) peroxide, di(perfluorovaleryl) peroxide, di(perfluorohexanoyl) peroxide, di(perfluoroheptanoyl) peroxide, di(perfluorooctanoyl) peroxide, di(perfluorononanoyl) peroxide, and di(ω-chloro Di[perfluoro(or fluorochloro)acyl]peroxides such as -hexafluorobutyryl)peroxide, di(ω-chloro-decafluorohexanoyl)peroxide, di(ω-chloro-tetradecafluorooctanoyl)peroxide, ω-hydro-dodecafluoroheptanoyl-ω-hydrohexadecafluorononanoyl-peroxide, ω-chloro-hexafluorobutyryl-ω-chloro-decafluorohexanoyl-peroxide, ω-hydrododecafluoroheptanoyl-perfluorobutyryl-peroxide, di(dichloropentafluorobutanoyl)peroxide, di(trichlorooctafluorohexanoyl)peroxide, di(tetrachloroundafluorooctanoyl)peroxide, di(pentachlorotetradecafluorodecanoyl)peroxide, and di(undachlorodotriacontafluorodocosanoyl)peroxide are typical examples.

[0074] The water-soluble radical polymerization initiator may be a known water-soluble peroxide, such as ammonium salts, potassium salts, and sodium salts of persulfuric acid, perboric acid, perchloric acid, superphosphate, and percarbonate, as well as t-butyl permalate, t-butyl hydroperoxide, and disuccinate peroxide. Among these, ammonium persulfate and disuccinate peroxide are preferred. Reducing agents such as sulfites and sulfites may also be included, and their amount may be 0.1 to 20 times the amount of the peroxide.

[0075] There are no particular limitations on the amount of water-soluble radical polymerization initiator added, but it is sufficient to add at least an amount that does not significantly reduce the polymerization rate (for example, several ppm relative to water concentration) in one lump sum at the beginning of polymerization, or sequentially or continuously. The upper limit is a range in which the reaction temperature may be increased while removing heat from the apparatus surface using the heat of the polymerization reaction, and a more preferable upper limit is a range in which the heat of the polymerization reaction can be removed from the apparatus surface. In order to easily obtain the physical properties described above, the amount of polymerization initiator added is preferably equivalent to 0.1 ppm or more relative to the aqueous medium, more preferably equivalent to 1.0 ppm or more, and preferably equivalent to 100 ppm or less, and more preferably equivalent to 10 ppm or less.

[0076] For example, when polymerization is carried out at low temperatures below 30°C, it is preferable to use a redox initiator that combines an oxidizing agent and a reducing agent as the polymerization initiator. Examples of oxidizing agents include persulfates, organic peroxides, potassium permanganate, manganese triacetate, ammonium cerium nitrate, and bromates. Examples of reducing agents include sulfites, bisulfites, bromates, diimines, and oxalic acid. Examples of persulfates include ammonium persulfate and potassium persulfate. Examples of sulfites include sodium sulfite and ammonium sulfite. To increase the decomposition rate of the initiator, it is also preferable to add copper salts and iron salts to the redox initiator combination. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate.

[0077] Preferably, the redox initiator described above is an oxidizing agent of permanganic acid or its salt, persulfate, manganese triacetate, cerium(IV) salt, or bromate or its salt, and the reducing agent is a dicarboxylic acid or its salt or diimine. More preferably, the oxidizing agent is permanganic acid or a salt thereof, a persulfate, or bromate or a salt thereof, and the reducing agent is a dicarboxylic acid or a salt thereof.

[0078] Examples of the redox initiators mentioned above include combinations such as potassium permanganate / oxalic acid, potassium permanganate / ammonium oxalate, manganese triacetate / oxalic acid, manganese triacetate / ammonium oxalate, cerium ammonium nitrate / oxalic acid, and cerium ammonium nitrate / ammonium oxalate. When using a redox initiator, either the oxidizing agent or the reducing agent may be placed in the polymerization tank beforehand, and then the other may be added continuously or intermittently to initiate polymerization. For example, when using potassium permanganate / ammonium oxalate, it is preferable to place ammonium oxalate in the polymerization tank and then continuously add potassium permanganate to it. In this specification, when "potassium permanganate / ammonium oxalate" is mentioned in reference to redox initiators, it refers to the combination of potassium permanganate and ammonium oxalate. The same applies to other compounds.

[0079] The above redox initiator is preferably a combination of an oxidizing agent that is a salt and a reducing agent that is a salt. For example, the oxidizing agent, which is a salt, is more preferably at least one selected from the group consisting of persulfates, permanganates, cerium(IV) salts, and bromates, with permanganates being even more preferred, and potassium permanganate being particularly preferred. Furthermore, the reducing agent, which is the salt mentioned above, is more preferably at least one selected from the group consisting of oxalates, malons, succinates, glutarates, and bromates, with oxalates being even more preferred, and ammonium oxalate being particularly preferred.

[0080] Specifically, the redox initiator described above is preferably at least one selected from the group consisting of potassium permanganate / oxalic acid, potassium permanganate / ammonium oxalate, potassium bromate / ammonium sulfite, manganese triacetate / ammonium oxalate, and cerium ammonium nitrate / ammonium oxalate; more preferably at least one selected from the group consisting of potassium permanganate / oxalic acid, potassium permanganate / ammonium oxalate, potassium bromate / ammonium sulfite, and cerium ammonium nitrate / ammonium oxalate; and even more preferably potassium permanganate / oxalic acid.

[0081] When using a redox initiator, the oxidizing agent and reducing agent may be added together at the beginning of polymerization, the reducing agent may be added together at the beginning of polymerization and the oxidizing agent may be added consecutively, the oxidizing agent may be added together at the beginning of polymerization and the reducing agent may be added consecutively, or both the oxidizing agent and reducing agent may be added consecutively.

[0082] When adding one of the above redox polymerization initiators in the initial stages of polymerization and continuously adding the other, it is preferable to gradually reduce the rate of addition in order to obtain PTFE with a low SSG, and it is even preferable to stop the addition midway through polymerization. The timing of stopping the addition is preferably before 20 to 40% by mass of the total TFE consumed in the polymerization reaction has been consumed.

[0083] When a redox initiator is used as a polymerization initiator, the amount of oxidizing agent added to the aqueous medium is preferably 0.1 ppm or more, more preferably 0.3 ppm or more, even more preferably 0.5 ppm or more, even more preferably 1.0 ppm or more, particularly preferably 5 ppm or more, especially preferably 10 ppm or more, and also preferably 10,000 ppm or less, more preferably 1,000 ppm or less, even more preferably 100 ppm or less, and even more preferably 10 ppm or less. The amount of reducing agent added is preferably 0.1 ppm or more, more preferably 1.0 ppm or more, even more preferably 3 ppm or more, even more preferably 5 ppm or more, particularly preferably 10 ppm or more, and also preferably 10,000 ppm or less, more preferably 1,000 ppm or less, even more preferably 100 ppm or less, and even more preferably 10 ppm or less. Furthermore, when a redox initiator is used in the emulsion polymerization described above, the polymerization temperature is preferably 100°C or lower, more preferably 95°C or lower, and even more preferably 90°C or lower. It is also preferably 10°C or higher, more preferably 20°C or higher, and even more preferably 30°C or higher.

[0084] As the polymerization initiators mentioned above, water-soluble radical polymerization initiators and redox initiators are preferred in that they improve binding strength, electrode strength, and electrode flexibility.

[0085] The above-mentioned aqueous medium is a reaction medium for polymerization and means a liquid containing water. The above-mentioned aqueous medium is not particularly limited as long as it contains water, and may contain water and, for example, a fluorine-free organic solvent such as an alcohol, ether, or ketone, and / or a fluorine-containing organic solvent with a boiling point of 40°C or less.

[0086] In the emulsion polymerization described above, nucleating agents, chain transfer agents, buffers, pH adjusters, stabilizing aids, dispersion stabilizers, radical scavengers, polymerization initiator decomposition agents, dicarboxylic acids, etc., may be used as needed.

[0087] The emulsion polymerization described above is preferably carried out with the addition of a nucleating agent for the purpose of adjusting the particle size. The nucleating agent is preferably added before the start of the polymerization reaction. The nucleating agent can be any known substance, and is preferably at least one selected from the group consisting of fluoropolyethers, nonionic surfactants, and chain transfer agents, with nonionic surfactants being more preferable.

[0088] Examples of the fluoropolyethers mentioned above include perfluoropolyether (PFPE) acids or salts thereof. The above-mentioned perfluoropolyether (PFPE) acid or its salt may have any chain structure in which the oxygen atoms in the main chain of the molecule are separated by saturated fluorinated carbon groups having 1 to 3 carbon atoms. Furthermore, two or more types of fluorinated carbon groups may be present in the molecule. A typical structure has repeating units represented by the following formula: (-CFCF3-CF2-O-) n (-CF2-CF2-CF2-O-) n (-CF2-CF2-O-) n -(-CF2-O-) m (-CF2-CFCF3-O-) n -(-CF2-O-) m

[0089] These structures are described by Kasai in J.Appl.Polymer Sci. 57,797 (1995). As disclosed in this document, the PFPE acid or salt thereof may have a carboxylic acid group or a salt thereof at one or both ends. The PFPE acid or salt thereof may also have a sulfonic acid, phosphonic acid group or a salt thereof at one or both ends. Furthermore, the PFPE acid or salt thereof may have different groups at each end. For monofunctional PFPE, the other end of the molecule is usually perfluorinated but may contain a hydrogen or chlorine atom. The PFPE acid or salt thereof has at least two ether oxygens, preferably at least four ether oxygens, and more preferably at least six ether oxygens. Preferably, at least one, more preferably at least two, of the fluorinated carbon groups separating the ether oxygens has two or three carbon atoms. More preferably, at least 50% of the fluorinated carbon groups separating the ether oxygen have 2 or 3 carbon atoms. Preferably, the PFPE acid or salt thereof has a total of at least 15 carbon atoms, and for example, the preferred minimum value of n or n+m in the repeating unit structure is at least 5. Two or more of the PFPE acid or salt thereof, each having an acid group at one or both ends, can be used in the manufacturing method of the present disclosure. Preferably, the PFPE acid or salt thereof has a number average molecular weight of less than 6000 g / mol.

[0090] The emulsion polymerization described above is preferably carried out with the addition of a radical scavenger or polymerization initiator decomposer, as this allows for further increasing the molecular weight of PTFE and improving the strength of the electrode mixture sheet. The radical scavenger or polymerization initiator decomposer is preferably added after the start of the polymerization reaction, preferably before 10% by mass or more, more preferably 20% by mass or more of the total TFE consumed in the polymerization reaction is polymerized, and preferably before 50% by mass or less, more preferably 40% by mass or less is polymerized. If depressurization and repressurization described later are performed, it is preferable to add the agent afterward.

[0091] The radical scavenger used is a compound that does not have the ability to restart after being added to or undergoing chain transfer with free radicals in the polymerization system. Specifically, the compound used is one that readily undergoes a chain transfer reaction with a primary radical or a growing radical and subsequently generates a stable radical that does not react with the monomer, or a compound that readily undergoes an addition reaction with a primary radical or a growing radical to generate a stable radical. Generally, what are called chain transfer agents are characterized by their activity in terms of chain transfer constant and restart efficiency. Among chain transfer agents, those with a restart efficiency of almost 0% are called radical scavengers. The radical scavenger described above can also be defined as a compound in which the chain transfer constant with TFE at polymerization temperature is greater than the polymerization rate constant, and the restart efficiency is substantially zero percent. "Substantially zero percent restart efficiency" means that the generated radicals make the radical scavenger a stable radical. Preferably, the compound has a chain transfer constant (Cs) with TFE at polymerization temperature (= chain transfer rate constant (kc) / polymerization rate constant (kp)) greater than 0.1, and more preferably, the compound has a chain transfer constant (Cs) of 0.5 or higher, even more preferably 1.0 or higher, even more preferably 5.0 or higher, and particularly preferably 10 or higher.

[0092] As the radical scavenger mentioned above, at least one selected from the group consisting of aromatic hydroxy compounds, aromatic amines, N,N-diethylhydroxylamine, quinone compounds, terpenes, thiocyanates, and cupric chloride (CuCl2) is preferred. Examples of aromatic hydroxy compounds include unsubstituted phenols, polyhydric phenols, salicylic acid, m- or p-salicylic acid, gallic acid, and naphthol. Examples of the unsubstituted phenols mentioned above include or-, m-, or p-nitrophenols, or-, m-, or p-aminophenols, and p-nitrosophenols. Examples of polyhydric phenols include catechol, resorcinol, hydroquinone, pyrogallol, phloroglucin, and naphthresorcinol. Examples of aromatic amines include or-, m-, or p-phenylenediamine and benzidine. Examples of the above-mentioned quinone compounds include or-, m-, or p-benzoquinone, 1,4-naphthoquinone, and alizarin. Examples of thiocyanates include ammonium thiocyanate (NH4SCN), potassium thiocyanate (KSCN), and sodium thiocyanate (NaSCN). Among the radical scavengers mentioned above, aromatic hydroxy compounds are preferred, unsubstituted phenols or polyhydric phenols are more preferred, and hydroquinones are even more preferred.

[0093] The amount of radical scavenger added is preferably 3 to 500% (molar basis) of the polymerization initiator concentration, from the viewpoint of moderately reducing the standard specific gravity. A more preferable lower limit is 10% (molar basis), and even more preferably 15% (molar basis). A more preferable upper limit is 400% (molar basis), and even more preferably 300% (molar basis).

[0094] The decomposition agent for the polymerization initiator can be any compound capable of decomposing the polymerization initiator used. For example, at least one selected from the group consisting of sulfites, bisulfites, bromates, diimines, diimines, oxalic acid, oxalates, copper salts, and iron salts is preferred. Examples of sulfites include sodium sulfite and ammonium sulfite. Examples of copper salts include copper(II) sulfate, and examples of iron salts include iron(II) sulfate. The amount of the above-mentioned decomposing agent added is preferably equivalent to 3 to 500% (molar basis) of the initiator concentration, from the viewpoint of moderately reducing the standard specific gravity. A more preferable lower limit is 10% (molar basis), and even more preferably 15% (molar basis). A more preferable upper limit is 400% (molar basis), and even more preferably 300% (molar basis).

[0095] The above emulsion polymerization may be carried out in the presence of 5 to 500 ppm of dicarboxylic acid relative to the aqueous medium, and preferably in the presence of 10 to 200 ppm of dicarboxylic acid, in order to reduce the amount of coagulated material produced during polymerization. If the amount of dicarboxylic acid is too little relative to the aqueous medium, sufficient effect may not be obtained, and if it is too much, a chain transfer reaction may occur, and the resulting polymer may have a low molecular weight. It is more preferable that the amount of dicarboxylic acid be 150 ppm or less. The dicarboxylic acid may be added before the start of the polymerization reaction or during the polymerization.

[0096] The above dicarboxylic acid is preferably one represented by the general formula: HOOCRCOOH (wherein R represents an alkylene group having 1 to 5 carbon atoms), more preferably succinic acid, malonic acid, glutaric acid, adipic acid, and pimelic acid, and even more preferably succinic acid.

[0097] In the emulsion polymerization described above, the polymerization temperature and polymerization pressure are appropriately determined depending on the type of monomer used, the molecular weight of the target PTFE, and the reaction rate. Typically, the polymerization temperature is 5 to 150°C, preferably 10°C or higher, more preferably 30°C or higher, and even more preferably 50°C or higher. Furthermore, 120°C or lower is more preferable, and 100°C or lower is even more preferable. The polymerization pressure is 0.05 to 10 MPaG. A polymerization pressure of 0.3 MPaG or higher is more preferable, and 0.5 MPaG or higher is even more preferable. Furthermore, 5.0 MPaG or lower is more preferable, and 3.0 MPaG or lower is even more preferable.

[0098] When VDF is used as the modified monomer, in the emulsion polymerization described above, it is preferable, and more preferable, for the VDF concentration in the reactor gas at the start of polymerization (when the initiator is added) to be 0.001 mol% or more, in order to easily obtain the above-mentioned physical properties. The above concentration may also be 15 mol% or less, preferably 6.0 mol% or less, more preferably 5.0 mol% or less, even more preferably 3.0 mol% or less, and particularly preferably 1.0 mol% or less. The above VDF concentration may be maintained thereafter until the end of the polymerization reaction, or depressurization may be performed during the reaction. It is preferable to charge the VDF all at once before the start of polymerization, but a portion may be added continuously or intermittently after the start of polymerization.

[0099] When VDF is used as the modified monomer, it is preferable not to depressurize the emulsion polymerization after adding the VDF to the polymerization vessel until the polymerization is complete. This allows the VDF to remain in the system until the end of polymerization, and the strength of the resulting electrode mixture sheet using PTFE can be further increased.

[0100] When HFP is used as a modified monomer, in the emulsion polymerization described above, it is preferable to set the HFP concentration in the reactor gas at the start of polymerization (when the initiator is added) to 0.01 to 3.0 mol%, as this allows for easy acquisition of the aforementioned physical properties. Furthermore, it is preferable that the HFP concentration in the reactor gas at the point when 40% by mass of the total TFE consumed in the polymerization reaction has been polymerized is greater than 0 mol% and 0.2 mol% or less. It is preferable to maintain the above HFP concentration until the end of the polymerization reaction. HFP may be charged all at once before the start of polymerization, or a portion may be charged before the start of polymerization and then continuously or intermittently added after the start of polymerization. By ensuring that HFP remains until the end of the polymerization reaction, the extrusion pressure is reduced despite the high strength of the resulting electrode mixture sheet using PTFE.

[0101] When HFP is used as the modified monomer, in the emulsion polymerization described above, it is preferable to depressurize 5 to 40% by mass of the total TFE consumed in the polymerization reaction before polymerization, and then repressurize using only TFE, in order to further improve the strength of the electrode mixture sheet using the resulting PTFE. The above depressurization is preferably carried out so that the pressure inside the reactor is 0.2 MPaG or less, more preferably 0.1 MPaG or less, and even more preferably 0.05 MPaG or less. It is also preferable to carry it out so that the pressure is 0.0 MPaG or more. Furthermore, the above depressurization and repressurization processes may be performed multiple times. Depressurization may also be carried out using a vacuum pump until the pressure is reduced.

[0102] When CTFE is used as the modified monomer, in the emulsion polymerization described above, it is preferable, and more preferable, for the CTFE concentration in the reactor gas at the start of polymerization (when the initiator is added) to be 0.001 mol% or more, in order to easily obtain the above-mentioned physical properties. The above concentration is also preferably 3.0 mol% or less, and more preferably 1.0 mol% or less. The above CTFE concentration may be maintained thereafter until the end of the polymerization reaction, or depressurization may be performed during the reaction. It is preferable to charge the CTFE all at once before the start of polymerization, but a portion may be added continuously or intermittently after the start of polymerization.

[0103] When using CTFE as a modified monomer, it is preferable not to depressurize the emulsion polymerization after adding the CTFE to the polymerization vessel until polymerization is complete. This allows the CTFE to remain in the system until the end of polymerization, and the strength of the resulting electrode mixture sheet using PTFE can be further increased.

[0104] The coagulation in step (B) can be carried out by known methods.

[0105] In step (C), the wet powder obtained in step (B) is placed in a container with a breathable bottom and / or sides, and heat-treated at a temperature of 130 to 300°C for at least two hours. By heat-treating under such extremely limited conditions, the fluorine-containing compounds with a molecular weight of 1000 or less can be efficiently removed along with water, and the content of the fluorine-containing compounds and water can be kept within the above-mentioned range.

[0106] The heat treatment temperature in step (C) is preferably 140°C or higher, more preferably 150°C or higher, even more preferably 160°C or higher, even more preferably 180°C or higher, even more preferably 200°C or higher, particularly preferably 220°C or higher, and also preferably 280°C or lower, and more preferably 250°C or lower, in order to remove moisture and fluorine-containing compounds more efficiently.

[0107] The heat treatment time in step (C) is preferably 5 hours or more, more preferably 10 hours or more, and even more preferably 15 hours or more, in order to remove moisture and fluorine-containing compounds more efficiently. There is no particular upper limit, but for example, it is preferably 100 hours, more preferably 50 hours, and even more preferably 30 hours.

[0108] In step (C), the air velocity is preferably 0.01 m / s or more, more preferably 0.03 m / s or more, even more preferably 0.05 m / s or more, and even more preferably 0.1 m / s or more, in order to remove moisture and fluorine-containing compounds more efficiently. Furthermore, in order to suppress powder scattering, the air velocity is preferably 50 m / s or less, more preferably 30 m / s or less, and even more preferably 10 m / s or less.

[0109] The heat treatment in step (C) can be carried out using an electric furnace or a steam furnace. For example, it can be carried out using an electric furnace such as a parallel flow box electric furnace, a ventilated box electric furnace, a ventilated conveyor electric furnace, a band electric furnace, a radiant conveyor electric furnace, a fluidized bed electric furnace, a vacuum electric furnace, agitated electric furnace, an airflow electric furnace, or a hot air circulation electric furnace, or a steam furnace corresponding to the above (an apparatus in which "electric furnace" in the apparatus name of each electric furnace is read as "steam furnace"). A parallel flow box electric furnace, a ventilated box electric furnace, a ventilated conveyor electric furnace, a band electric furnace, a fluidized bed electric furnace, a hot air circulation electric furnace, or a steam furnace corresponding to the above (an apparatus in which "electric furnace" in the apparatus name of each electric furnace is read as "steam furnace") is preferred in that it can remove moisture and fluorine-containing compounds more efficiently.

[0110] The heat treatment in step (C) is carried out by placing the wet powder in a container with a breathable bottom and / or sides. The container with a breathable bottom and / or sides can be any container capable of withstanding the heat treatment temperature, but it is preferable that it be made of metal such as stainless steel. As for the above-mentioned container with a breathable bottom and / or sides, a tray (bath) with a breathable bottom and / or sides is preferred, and a tray (mesh tray) with a mesh bottom and / or sides is even more preferred. The above mesh is preferably either woven mesh or perforated metal. The mesh opening of the above mesh is preferably 2000 μm or less (10 mesh or more according to ASTM standards), more preferably 595 μm or less (30 mesh or more), even more preferably 297 μm or less (50 mesh or more), even more preferably 177 μm or less (80 mesh or more), especially preferably 149 μm or less (100 mesh or more), and particularly preferably 74 μm or less (200 mesh or more). Also, 25 μm or more (500 mesh or less) is preferred. Examples of weaving methods for the above mesh if it is a woven net include plain weave, twill weave, plain tatami weave, and twill tatami weave. When the above mesh is perforated metal, the perforation rate is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more. Also, 95% or less is preferred.

[0111] In step (C), the amount of the wet powder is 10 g / cm³, which allows for more efficient removal of moisture and fluorine-containing compounds. 2 Preferably, it is 8 g / cm³ 2 More preferably, it is 5 g / cm³. 2 It is even more preferable that the following conditions apply: 3 g / cm³ 2 It is particularly preferable that the following conditions be met, and also 0.01 g / cm³ 2 Preferably, it is 0.05 g / cm³ or more. 2 It is more preferable that the concentration be greater than or equal to 0.1 g / cm³. 2 It is even more preferable that the above conditions are met.

[0112] In step (C), the moisture content of the wet powder subjected to heat treatment is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and preferably 150% by mass or less, and more preferably 100% by mass or less, in order to remove moisture and fluorine-containing compounds more efficiently.

[0113] The PTFE powder of this disclosure is used as an electrode binder. In the electrode binder, the PTFE powder of this disclosure may be used alone or mixed with other materials (for example, polymers other than PTFE), but it is preferable, and more preferable, to use the PTFE powder of this disclosure substantially alone. Using the PTFE powder of this disclosure substantially alone means using it in such a way that the amount of PTFE powder in the electrode binder is within the range described later.

[0114] This disclosure provides an electrode binder consisting substantially of PTFE powder, wherein the PTFE powder substantially does not contain water or fluorine-containing compounds with a molecular weight of 1000 or less. The binder of this disclosure, because it contains specific PTFE powder, is a sustainable product and can suppress gas generation inside the battery cell and degradation of battery characteristics (e.g., decrease in capacity during high-temperature storage). It can also improve electrode strength. Furthermore, since it can be mixed with the electrode active material in powder form, there is no need to use organic solvents, thus reducing processes and costs associated with the use of organic solvents.

[0115] The PTFE powder used in the binder of this disclosure may be the same as the PTFE powder described above, and the preferred embodiments are also the same.

[0116] The binder of this disclosure consists substantially of the above-mentioned PTFE powder. This allows the effects of the above-mentioned PTFE powder to be significantly exhibited. "Consisting substantially of the above-mentioned PTFE powder" means that the content of the above-mentioned PTFE powder is 95.0% by mass or more relative to the binder. The content of the PTFE powder is preferably 98.0% by mass or more, more preferably 99.0% by mass or more, even more preferably 99.5% by mass or more, particularly preferably 99.9% by mass or more, and most preferably 99.95% by mass or more, relative to the binder. It is also preferable that the binder of this disclosure consists solely of the above-mentioned PTFE powder.

[0117] The binder of this disclosure is preferably substantially free of organic solvents. This reduces the process and costs associated with the use of organic solvents. Substantially free of organic solvents means that the organic solvent content in the binder is 5% by mass or less. The organic solvent content is preferably 3% by mass or less, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, even more preferably 0.01% by mass or less, and particularly preferably 0.001% by mass or less.

[0118] The binder of this disclosure is preferably in the form of a powder.

[0119] The binder of this disclosure can be suitably used as an electrode binder for secondary batteries such as lithium-ion batteries.

[0120] This disclosure also provides an electrode mixture comprising the PTFE powder or electrode binder described herein and an electrode active material. Using the electrode mixture of this disclosure, an electrode can be obtained that is a sustainable product and can suppress gas generation inside the battery cell and degradation of battery characteristics (e.g., decrease in capacity when stored at high temperatures). It can also improve electrode strength. Furthermore, it can retain the electrode active material even with a small amount of binder.

[0121] Examples of the electrode active materials mentioned above include positive electrode active materials and negative electrode active materials.

[0122] The positive electrode active material is not particularly limited as long as it is electrochemically capable of intercalating and releasing alkali metal ions, but for example, a material containing an alkali metal and at least one transition metal is preferred. Specific examples include alkali metal-containing transition metal composite oxides, alkali metal-containing transition metal phosphate compounds, and conductive polymers. Among these, alkali metal-containing transition metal composite oxides that produce high voltage are particularly preferred as the positive electrode active material. Examples of the alkali metal ions include lithium ions, sodium ions, and potassium ions. In a preferred embodiment, the alkali metal ion may be a lithium ion. That is, in this embodiment, the alkali metal ion secondary battery is a lithium ion secondary battery.

[0123] Examples of the alkali metal-containing transition metal composite oxides mentioned above include: Formula:M a Mn 2-b M 1 b O4 (wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0.9 ≤ a; 0 ≤ b ≤ 1.5; M) 1Lithium-manganese spinel composite oxide represented by at least one metal selected from the group consisting of Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge. Formula:MNi 1-c M 2 c O2 (wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0 ≤ c ≤ 0.5; M 2 (This refers to a lithium-nickel composite oxide represented by at least one metal selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge), or Formula:MCo 1-d M 3 d O2 (wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0 ≤ d ≤ 0.5; M 3 Examples include lithium-cobalt composite oxides represented by at least one metal selected from the group consisting of Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge. In the above, M is preferably one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li.

[0124] In particular, MCoO2, MMnO2, MNiO2, MMn2O4, and MNi are used because they offer high energy density and can provide high-output secondary batteries. 0.8 Co 0.15 Al 0.05 O2, or MNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 is preferred, and it is preferable that the compound is represented by the following general formula (3). MNi h Co i Mn j M 5 k O2(3) (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, and M 5 represents at least one selected from the group consisting of Fe, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge, and (h + i + j + k) = 1.0, 0 ≦ h ≦ 1.0, 0 ≦ i ≦ 1.0, 0 ≦ j ≦ 1.5, 0 ≦ k ≦ 0.2.)

[0125] Examples of the alkali metal-containing transition metal phosphate compound include, for example, the following formula (4): M e M 4 f (PO4) g (4) (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, and M 4 represents at least one selected from the group consisting of V, Ti, Cr, Mn, Fe, Co, Ni, and Cu, and 0.5 ≦ e ≦ 3, 1 ≦ f ≦ 2, 1 ≦ g ≦ ) Compounds represented by 3 are exemplified. In the above, M is preferably one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li.

[0126] As the transition metal of the lithium-containing transition metal phosphate compound, V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. are preferable. Specific examples include, for example, iron phosphates such as LiFePO4, Li3Fe2(PO4)3, LiFeP2O7, cobalt phosphates such as LiCoPO4, and those in which a part of the transition metal atoms that are the main components of these lithium transition metal phosphate compounds are substituted with other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si, etc. The lithium-containing transition metal phosphate compound preferably has an olivine-type structure.

[0127] The other positive electrode active materials include MFePO4, MNi 0.8 Co 0.2 O2, M 1.2 Fe 0.4 Mn 0.4 0.4O2, MNi 0.5 Mn 1.5 Examples include O2, MV3O6, M2MnO3, etc. In particular, M2MnO3, MNi 0.5 Mn 1.5 Positive electrode active materials such as O2 are preferable in that the crystal structure does not collapse even when the secondary battery is operated at a voltage exceeding 4.4 V or a voltage of 4.6 V or higher. Therefore, an electrochemical device such as a secondary battery using a positive electrode material containing the positive electrode active material exemplified above is preferable because the residual capacity hardly decreases and the resistance increase rate hardly changes even when stored at a high temperature, and the battery performance does not deteriorate even when operated at a high voltage.

[0128] As other positive electrode active materials, M2MnO3 and MM 6 O2 (where M is at least one metal selected from the group consisting of Li, Na, and K, and M 6 is a transition metal such as Co, Ni, Mn, Fe, etc.) and solid solution materials thereof can also be mentioned.

[0129] Examples of the solid solution material include, for example, an alkali metal manganate represented by the general formula Mx[Mn (1-y) M 7 y O z Here, M in the formula is at least one metal selected from the group consisting of Li, Na, and K, and M 7 consists of at least one metal element other than M and Mn, and includes, for example, one or more elements selected from the group consisting of Co, Ni, Fe, Ti, Mo, W, Cr, Zr, and Sn. Also, the values of x, y, and z in the formula are in the range of 1 < x < 2, 0 ≤ y < 1, and 1.5 < z < 3. Among them, a manganese-containing solid solution material in which LiNiO2 or LiCoO2 is solid-solved based on Li2MnO3 such as Li 1.2 Mn 0.5 Co 0.14 Ni 0.14 O2 is preferable in that it can provide an alkali metal ion secondary battery having a high energy density.

[0130] Furthermore, including lithium phosphate in the positive electrode active material is preferable because it improves continuous charging characteristics. There are no restrictions on the use of lithium phosphate, but it is preferable to use a mixture of the positive electrode active material and lithium phosphate. The amount of lithium phosphate used is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, relative to the total amount of the positive electrode active material and lithium phosphate, with an upper limit of preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less.

[0131] Examples of the conductive polymers mentioned above include p-doped and n-doped conductive polymers. Examples of conductive polymers include polyacetylene-based polymers, polyphenylene-based polymers, heterocyclic polymers, ionic polymers, ladder and network polymers, etc.

[0132] Furthermore, a positive electrode active material may be used in which a substance of a different composition is attached to its surface. Examples of surface-attached substances include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0133] These surface-adhering substances can be attached to the surface of the positive electrode active material by, for example, dissolving or suspending them in a solvent and impregnating them into the positive electrode active material, followed by drying; dissolving or suspending a surface-adhering substance precursor in a solvent and impregnating it into the positive electrode active material, then reacting it by heating or other means; or adding it to the positive electrode active material precursor and simultaneously firing it. When attaching carbon, a method of mechanically attaching carbonaceous material afterwards, such as activated carbon, can also be used.

[0134] The amount of surface-adhered material is preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 10 ppm or more, relative to the positive electrode active material by mass, with an upper limit of preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. The surface-adhered material can suppress the oxidation reaction of the electrolyte on the surface of the positive electrode active material, thereby improving battery life. However, if the amount of adhesion is too small, the effect will not be fully realized, and if it is too large, it may hinder the movement of lithium ions in and out, potentially increasing resistance.

[0135] The particle shapes of the positive electrode active material can include conventionally used shapes such as lumpy, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar. Furthermore, primary particles may aggregate to form secondary particles.

[0136] The tap density of the positive electrode active material is preferably 0.5 g / cm³. 3 More preferably 0.8 g / cm³ 3 More preferably 1.0 g / cm³ 3 The above is the case. If the tap density of the positive electrode active material falls below the above lower limit, the amount of dispersion medium required during the formation of the positive electrode active material layer increases, as does the amount of conductive material and binder required, which may restrict the filling rate of the positive electrode active material into the positive electrode active material layer and thus limit the battery capacity. By using a composite oxide powder with a high tap density, a high-density positive electrode active material layer can be formed. Generally, a higher tap density is preferable, and there is no particular upper limit, but if it is too high, the diffusion of lithium ions using the electrolyte as a medium within the positive electrode active material layer becomes the rate-limiting step, which may lead to a decrease in load characteristics. Therefore, the upper limit is preferably 4.0 g / cm³. 3 More preferably, 3.7 g / cm³ 3 More preferably, 3.5 g / cm³ 3 The following applies: The tap density mentioned above is the powder packing density (tap density) g / cm³ obtained when 5-10 g of positive electrode active material powder is placed in a 10 ml glass graduated cylinder and tapped 200 times with a stroke of approximately 20 mm. 3 We will seek it as follows.

[0137] The median diameter d50 of the positive electrode active material particles (or secondary particle diameter if primary particles aggregate to form secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and most preferably 1.0 μm or more. It is also preferably 30 μm or less, more preferably 27 μm or less, even more preferably 25 μm or less, and most preferably 22 μm or less. If it falls below the lower limit, it may not be possible to obtain a high tap density product, and if it exceeds the upper limit, the diffusion of lithium within the particles will take longer, which may lead to a decrease in battery performance or problems such as streaking when creating the positive electrode of the battery, i.e., when slurrying the active material with conductive material and binder etc. in a solvent and coating it into a thin film. Here, by mixing two or more of the above positive electrode active materials having different median diameters d50, the packing performance during positive electrode creation can be further improved.

[0138] The above median diameter d50 is measured using a known laser diffraction / scattering particle size distribution analyzer. When using the HORIBA LA-920 as the particle size distribution analyzer, a 0.1 mass% sodium hexametaphosphate aqueous solution is used as the dispersion medium during measurement, and the measurement is performed after ultrasonic dispersion for 5 minutes with the measurement refractive index set to 1.24.

[0139] When primary particles aggregate to form secondary particles, the average primary particle diameter of the positive electrode active material is preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. The upper limit is preferably 5 μm or less, more preferably 4 μm or less, even more preferably 3 μm or less, and most preferably 2 μm or less. Exceeding the upper limit makes it difficult to form spherical secondary particles, which can adversely affect powder packing properties and significantly reduce the specific surface area, potentially leading to a decrease in battery performance such as output characteristics. Conversely, below the lower limit usually results in problems such as poor reversibility of charge and discharge due to underdeveloped crystals. The average primary particle diameter mentioned above is measured by observation using a scanning electron microscope (SEM). Specifically, it is determined by taking a 10,000x magnification photograph, finding the longest value of the intercept between the left and right boundaries of the primary particle relative to a horizontal line for any 50 primary particles, and then taking the average value.

[0140] The BET specific surface area of ​​the positive electrode active material is preferably 0.1 m². 2 / g or more, more preferably 0.2m 2 / g or more, more preferably 0.3m 2 The value is 1 / g or more, and the upper limit is preferably 50m 2 / g or less, more preferably 40m 2 / g or less, more preferably 30m 2 It is less than / g. If the BET specific surface area is smaller than this range, battery performance tends to decrease, and if it is larger, it becomes difficult to increase the tap density, which can cause problems with coating when forming the positive electrode active material layer. The above BET specific surface area is defined as the value measured by a single-point nitrogen adsorption BET method using a gas flow method, after pre-drying the sample at 150°C for 30 minutes under nitrogen flow using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.), and then using a nitrogen-helium mixed gas that has been precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3.

[0141] When the secondary battery of this disclosure is used as a large lithium-ion secondary battery for hybrid vehicles or distributed power sources, high output is required, so it is preferable that the particles of the positive electrode active material consist mainly of secondary particles. It is preferable that the particles of the positive electrode active material contain 0.5 to 7.0 volume percent of fine particles, the average particle diameter of the secondary particles being 40 μm or less and the average primary particle diameter being 1 μm or less. By including fine particles with an average primary particle diameter of 1 μm or less, the contact area with the electrolyte is increased, the diffusion of lithium ions between the electrode mixture and the electrolyte can be accelerated, and as a result, the output performance of the battery can be improved.

[0142] For the production of positive electrode active materials, general methods for producing inorganic compounds are used. In particular, various methods can be considered for producing spherical or ellipsoidal active materials. For example, a method can be used in which transition metal raw materials are dissolved or pulverized and dispersed in a solvent such as water, the pH is adjusted while stirring to create and recover spherical precursors, these are dried as needed, and then a Li source such as LiOH, Li2CO3, or LiNO3 is added and calcined at a high temperature to obtain the active material.

[0143] For the manufacture of the positive electrode, the positive electrode active material may be used alone, or two or more materials with different compositions may be used in any combination or ratio. In this case, a preferred combination is LiCoO2 and LiNi 0.33 Co 0.33 Mn 0.33 Examples include combinations with ternary systems such as O2, combinations of LiCoO2 and LiMn2O4 or a combination in which part of the Mn is substituted with other transition metals, or combinations of LiFePO4 and LiCoO2 or a combination in which part of the Co is substituted with other transition metals.

[0144] The content of the positive electrode active material is preferably 50 to 99.5% by mass of the positive electrode mixture, and more preferably 80 to 99% by mass, in order to achieve high battery capacity. Furthermore, the content in the positive electrode active material layer is preferably 80% by mass or more, more preferably 82% by mass or more, and particularly preferably 84% by mass or more. The upper limit is preferably 99% by mass or less, and more preferably 98% by mass or less. If the content of the positive electrode active material in the positive electrode active material layer is too low, the electrical capacity may be insufficient. Conversely, if the content is too high, the strength of the positive electrode may be insufficient.

[0145] The negative electrode active material is not particularly limited and includes, for example, lithium metal, artificial graphite, graphite carbon fiber, resin-fired carbon, pyrolysis vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-fired carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, and carbonaceous materials such as non-graphitizable carbon, silicon and silicon alloys, silicon-containing compounds, Li4Ti5O 12Examples include any of the above, or a mixture of two or more types. Among these, materials containing at least a portion of carbonaceous material, or silicon-containing compounds, can be used particularly suitably.

[0146] The negative electrode active material used in this disclosure preferably contains silicon as a constituent element. By including silicon as a constituent element, a high-capacity battery can be manufactured.

[0147] Preferred silicon-containing materials include silicon particles, particles having a structure in which silicon fine particles are dispersed in a silicon-based compound, silicon oxide particles represented by the general formula SiOx (0.5 ≤ x ≤ 1.6), or mixtures thereof. Using these materials makes it possible to obtain a negative electrode mixture for lithium-ion secondary batteries that has higher initial charge-discharge efficiency, higher capacity, and excellent cycle characteristics.

[0148] In this disclosure, silicon oxide refers to a general term for amorphous silicon oxides, and silicon oxide before disproportionation is represented by the general formula SiOx (0.5 ≤ x ≤ 1.6). x is preferably 0.8 ≤ x < 1.6, and more preferably 0.8 ≤ x < 1.3. This silicon oxide can be obtained, for example, by heating a mixture of silicon dioxide and metallic silicon to produce silicon monoxide gas, which is then cooled and precipitated.

[0149] Particles having a structure in which silicon nanoparticles are dispersed in a silicon-based compound can be obtained, for example, by calcining a mixture of silicon nanoparticles and a silicon-based compound, or by heat-treating silicon oxide particles before disproportionation, represented by the general formula SiOx, in an inert, non-oxidizing atmosphere such as argon at a temperature of 400°C or higher, preferably 800-1,100°C, to carry out a disproportionation reaction. The material obtained by the latter method is particularly preferable because the silicon microcrystals are uniformly dispersed. Through the disproportionation reaction described above, the size of the silicon nanoparticles can be made to 1-100 nm. It is desirable that the silicon oxide in the particles having a structure in which silicon nanoparticles are dispersed in silicon oxide is silicon dioxide. Furthermore, it can be confirmed by transmission electron microscopy that silicon nanoparticles (crystals) are dispersed in amorphous silicon oxide.

[0150] The physical properties of silicon-containing particles can be appropriately selected depending on the target composite particle. For example, the average particle size is preferably 0.1 to 50 μm, the lower limit is more preferably 0.2 μm or more, and even more preferably 0.5 μm or more. The upper limit is more preferably 30 μm or less, and even more preferably 20 μm or less. The above average particle size is expressed as the weight-average particle size measured by the particle size distribution method using laser diffraction.

[0151] BET specific surface area is 0.5-100m 2 / g is preferred, 1 to 20m 2 / g is more preferable. BET specific surface area is 0.5m² 2 If the value is 1 / g or higher, there is no risk of reduced adhesion to the electrodes and a decrease in battery performance. Also, 100m 2 If the value is less than / g, the proportion of silicon dioxide on the particle surface will be high, and there will be no risk of a decrease in battery capacity when used as a negative electrode material for lithium-ion secondary batteries.

[0152] By carbon coating the silicon-containing particles mentioned above, conductivity is imparted, resulting in improved battery characteristics. Methods for imparting conductivity include mixing with conductive particles such as graphite, coating the surface of the silicon-containing particles with a carbon film, and combining both methods. However, coating with a carbon film is preferred, and chemical vapor deposition (CVD) is more preferred.

[0153] The content of the above-mentioned negative electrode active material is preferably 40% by mass or more, more preferably 50% by mass or more, and particularly preferably 60% by mass or more, in order to increase the volume of the resulting electrode mixture. The upper limit is preferably 99% by mass or less, and more preferably 98% by mass or less.

[0154] The electrode mixture of this disclosure preferably further includes a conductive additive. As the above conductive assistant, known conductive materials can be arbitrarily used. Specific examples include metal materials such as copper and nickel, graphite (graphite) such as natural graphite and artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon materials such as needle coke, carbon nanotubes, fullerenes, and amorphous carbons such as VGCF. These may be used alone or in combination of two or more in any combination and ratio.

[0155] The conductive assistant is usually used at 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more in the electrode mixture, and usually 50% by mass or less, preferably 30% by mass or less, more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

[0156] The electrode mixture of the present disclosure may further contain a thermoplastic resin. Examples of the thermoplastic resin include polyvinylidene fluoride, polypropylene, polyethylene, polystyrene, polyethylene terephthalate, polyethylene oxide, etc. It may be used alone or in combination of two or more in any combination and ratio.

[0157] The ratio of the thermoplastic resin to the electrode active material is usually in the range of 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.10% by mass or more, and usually 3.0% by mass or less, preferably 2.5% by mass or less, more preferably 2.0% by mass or less. By adding the thermoplastic resin, the mechanical strength of the electrode can be improved. Also, if it exceeds this range, the proportion of the electrode active material in the electrode mixture may decrease, and problems such as a decrease in the battery capacity and an increase in the resistance between the active materials may occur.

[0158] In the electrode binder of the present disclosure, the content of the binder may be 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and may be 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 10% by mass or less, particularly preferably 5% by mass or less, and most preferably 3% by mass or less, based on the electrode binder. If the proportion of the binder is too low, the electrode active material cannot be sufficiently retained, resulting in insufficient mechanical strength of the electrode binder sheet and deterioration of battery performance such as cycle characteristics. On the other hand, if it is too high, it may lead to a decrease in battery capacity and conductivity. Since the binder of the present disclosure has excellent adhesive strength, the electrode active material can be sufficiently retained even with a small content.

[0159] In the electrode binder of the present disclosure, the binder component preferably consists substantially of only the above PTFE powder, and more preferably consists of only the above PTFE powder. That the binder component consists substantially of only the above PTFE powder means that the content of the above PTFE powder in the binder component constituting the electrode binder is 95.0% by mass or more based on the binder component. The content of the above PTFE powder is preferably 98.0% by mass or more, more preferably 99.0% by mass or more, further preferably 99.5% by mass or more, particularly preferably 99.9% by mass or more, and most preferably 99.95% by mass or more, based on the binder component.

[0160] The electrode binder of the present disclosure is preferably in the form of a sheet.

[0161] The electrode binder of the present disclosure can be preferably used as an electrode binder for secondary batteries. In particular, the electrode binder of the present disclosure is suitable for lithium-ion secondary batteries. When used in secondary batteries, the electrode binder of the present disclosure is usually used in the form of a sheet.

[0162] The following is an example of a specific manufacturing method for an electrode mixture sheet containing an electrode mixture. The above electrode mixture sheet can be obtained by a manufacturing method comprising: (1) mixing a raw material composition containing an electrode active material, a binder, and optionally a conductive additive; (2) forming the raw material composition obtained in step (1) into a bulk form; and (3) rolling the bulk raw material composition obtained in step (2) into a sheet form.

[0163] At the stage in step (1) above where the raw material composition is mixed, the raw material composition exists in a state without a defined form, with the electrode active material, binder, etc., simply mixed together. Specific mixing methods include using a W-type mixer, V-type mixer, drum-type mixer, ribbon mixer, conical screw-type mixer, single-shaft kneader, twin-shaft kneader, mix morar, agitator mixer, planetary mixer, etc.

[0164] In step (1) above, the binder mixing conditions are preferably 1000 rpm or less. Preferably 10 rpm or more, more preferably 15 rpm or more, even more preferably 20 rpm or more, and also preferably in the range of 900 rpm or less, more preferably 800 rpm or less, and even more preferably 700 rpm or less. If the speed is below the above range, mixing will take a long time and will affect productivity. If the speed is above the above range, fibrillation may proceed excessively, which may result in an electrode mixture sheet with poor strength and flexibility.

[0165] In step (2) above, "forming into a bulk form" means forming the raw material composition into a single mass. Specific methods for forming into a bulk form include extrusion molding and press molding. Furthermore, "bulk form" does not specify a particular shape; it simply means being in a single mass-like state, and includes forms such as rods, sheets, spheres, and cubes.

[0166] Specific rolling methods in step (3) above include methods using a roll press, a flat plate press, a calender roll machine, etc.

[0167] Furthermore, it is preferable to have a step (4) after step (3) in which a greater load is applied to the obtained rolled sheet and it is further rolled into a thinner sheet. It is also preferable to repeat step (4). In this way, rather than thinning the rolled sheet all at once, rolling it little by little in stages results in better flexibility. The number of times step (4) is performed is preferably 2 to 10 times, and more preferably 3 to 9 times. Specific rolling methods include, for example, a method in which two or more rolls are rotated and the rolled sheet is passed between them to process it into a thinner sheet.

[0168] Furthermore, from the viewpoint of adjusting the fibril diameter, it is also preferable to have a step (5) after step (3) or step (4) in which the rolled sheet is roughly crushed, then reshaped into a bulk form, and rolled into a sheet form again. It is also preferable to repeat step (5). The number of times step (5) is performed is preferably 1 to 12 times, and more preferably 2 to 11 times.

[0169] In step (5), specific methods for roughly crushing the rolled sheet and forming it into a bulk form include folding the sheet, forming it into a rod or thin film sheet, or chipping it. In this disclosure, "rough crushing" means changing the form of the rolled sheet obtained in step (3) or step (4) to another form in order to roll it into a sheet in the next step, and includes cases such as simply folding the rolled sheet.

[0170] Furthermore, step (4) may be performed after step (5), and this process may be repeated. Also, uniaxial stretching or biaxial stretching may be performed in steps (2) to (3), (4), and (5). In addition, the fibril diameter can be adjusted by the degree of coarse crushing in step (5).

[0171] In the above steps (3), (4), or (5), the rolling ratio is preferably 10% or more, more preferably 20% or more, and also preferably in the range of 80% or less, more preferably 65% ​​or less, and even more preferably 50% or less. If it is below the above range, the time will increase with the number of rolling cycles, affecting productivity. If it is above, fibrillation will proceed excessively, and there is a risk that the electrode mixture sheet will have poor strength and flexibility. The rolling ratio referred to here is the rate of decrease in thickness after processing relative to the thickness of the sample before rolling. The sample before rolling may be a bulk raw material composition or a sheet raw material composition. The thickness of the sample refers to the thickness in the direction in which the load is applied during rolling.

[0172] The above electrode mixture sheet is Step (a): A step of mixing powder components and a binder to form an electrode mixture, Step (b): A step of manufacturing a sheet by calendering or extruding the electrode mixture. Includes, The mixing in step (a) is (a1) A process of homogenizing the powder components and binder to make a powder, (a2) A step of preparing an electrode mixture by mixing the powdered raw material mixture obtained in step (a1) It can also be suitably manufactured by a manufacturing method characterized by including [the specified element].

[0173] For example, PTFE has two transition temperatures, at approximately 19°C and 30°C. Below 19°C, PTFE can be easily mixed while maintaining its shape. However, above 19°C, the structure of PTFE particles loosens, making them more sensitive to mechanical shear. Above 30°C, a higher degree of fibrillation occurs.

[0174] Therefore, it is preferable to perform the homogenization of (a1) at a temperature of 19°C or lower, preferably 0°C to 19°C. In other words, in such (a1), it is preferable to mix and homogenize while suppressing fibrillation. In the mixing in step (a2) which is the subsequent step, it is preferable to promote fibrillation by performing the mixing at a temperature of 30°C or higher.

[0175] The above step (a2) is preferably carried out at a temperature of 30°C to 150°C, more preferably 35°C to 120°C, and even more preferably 40°C to 80°C. In one embodiment, the calendaring or extrusion in the above step (b) is carried out at a temperature between 30°C and 150°C, preferably between 35°C and 120°C, and more preferably between 40°C and 100°C.

[0176] The mixing in the above step (a) is preferably carried out while applying a shearing force. Specific mixing methods include methods of mixing using a W-type mixer, a V-type mixer, a drum-type mixer, a ribbon mixer, a conical screw-type mixer, a single-screw kneader, a twin-screw kneader, a mix muller, a stirring mixer, a planetary mixer, a Henschel mixer, a high-speed mixer, etc.

[0177] The mixing conditions may be appropriately set for the rotation speed and the mixing time. For example, the rotation speed is preferably 15000 rpm or less. Preferably it is 10 rpm or more, more preferably 1000 rpm or more, even more preferably 3000 rpm or more, and also preferably 12000 rpm or less, more preferably 11000 rpm or less, and even more preferably within the range of 10000 rpm. If it is below the above range, it will take time for mixing and affect productivity. Also, if it exceeds the range, fibrillation may proceed excessively and there is a risk of obtaining an electrode binder sheet with poor strength. In step (a1), it is preferable to carry out the process with a shearing force weaker than that in step (a2).

[0178] In the above step (a2), it is preferable that the raw material composition does not contain a liquid solvent, but a small amount of lubricant may be used. That is, a lubricant may be added to the powdery raw material mixture obtained by the above step (a1) to prepare a paste.

[0179] The above lubricants are not particularly limited and include water, ether compounds, alcohols, ionic liquids, carbonates, aliphatic hydrocarbons (low-polarity solvents such as heptane and xylene), isoparaffinic hydrocarbon compounds, and petroleum fractions (gasoline (C4-C10), naphtha (C4-C11), kerosene / paraffin (C10-C16), and mixtures thereof).

[0180] The above lubricant preferably has a water content of 1000 ppm or less. A moisture content of 1000 ppm or less is preferable in that it reduces the degradation of electrochemical devices. A moisture content of 500 ppm or less is even more preferable.

[0181] When using the above-mentioned lubricant, it is particularly preferable that it be a low-polarity solvent such as heptane or xylene, or an ionic liquid.

[0182] When using the above lubricant, the amount may be 5.0 to 35.0 parts by weight, preferably 10.0 to 30.0 parts by weight, and more preferably 15.0 to 25.0 parts by weight, relative to the total weight of the composition subjected to step (a1).

[0183] The above raw material composition preferably contains substantially no liquid medium. Conventional methods for forming electrode mixtures generally involve preparing a slurry in which powder components of the electrode mixture are dispersed using a solvent in which the binder is dissolved, and then preparing an electrode mixture sheet by coating and drying the slurry. In this case, a solvent that dissolves the binder is used. However, conventional solvents that can dissolve binder resins are limited to specific solvents such as butyl butyrate. These react with solid electrolytes and degrade them, which can lead to a decrease in battery performance. Furthermore, with low-polarity solvents such as heptane, the binder resins that can be dissolved are very limited, and their low flash points can make handling cumbersome.

[0184] By using a low-moisture powder binder instead of a solvent during electrode compound sheet formation, it is possible to manufacture batteries with less degradation of the solid electrolyte. Furthermore, in the above manufacturing method, it is possible to manufacture electrode compound sheets containing a binder with a fine fibrous structure, and the burden of the manufacturing process can be reduced by not having to prepare a slurry.

[0185] Step (b) is calendering or extrusion. Calendering and extrusion can be carried out by well-known methods. This allows the electrode mixture to be formed into the shape of a sheet. Step (b) preferably includes (b1) a step of forming the electrode mixture obtained in step (a) into a bulk form, and (b2) a step of calendering or extruding the bulk electrode mixture.

[0186] Forming into a bulk form means creating a single mass from the electrode mixture. Specific methods for forming materials into bulk include extrusion molding and press molding. Furthermore, "bulk form" does not specify a particular shape, but rather refers to a state in which there is a single mass, and includes forms such as rod-shaped, sheet-shaped, spherical, and cube-shaped. The size of the mass is preferably such that the diameter of its cross-section or the shortest side is 10,000 μm or more. More preferably, it is 20,000 μm or more.

[0187] Specific methods for calendering or extrusion molding in the above process (b2) include rolling the electrode mixture using a roll press, calender roll machine, etc.

[0188] Step (b) described above is preferably carried out at 30 to 150°C. As mentioned above, PTFE has a glass transition temperature of around 30°C, and therefore readily undergoes fibrillation at temperatures above 30°C. For this reason, step (b) is preferably carried out at such temperatures.

[0189] During calendering or extrusion, shear forces are applied, which causes the PTFE to fibrillate, resulting in the formation of the molded material.

[0190] It is also preferable to have a step (c) after step (b) in which a larger load is applied to the obtained rolled sheet and it is further rolled into a thinner sheet. It is also preferable to repeat step (c). In this way, rather than thinning the rolled sheet all at once, rolling it little by little in stages results in better flexibility. The number of times step (c) is performed is preferably 2 to 10 times, and more preferably 3 to 9 times. Specific rolling methods include, for example, a method in which two or more rolls are rotated and the rolled sheet is passed between them to process it into a thinner sheet.

[0191] Furthermore, from the viewpoint of adjusting the sheet strength, it is also preferable to have a step (d) after step (b) or step (c) in which the rolled sheet is roughly crushed, then reshaped into a bulk form, and rolled into a sheet form again. It is also preferable to repeat step (d). The number of times step (d) is performed is preferably 1 to 12 times, and more preferably 2 to 11 times.

[0192] In step (d), specific methods for roughly crushing the rolled sheet and forming it into a bulk form include folding the rolled sheet, forming it into a rod or thin film sheet, or chipping it. In this disclosure, "rough crushing" means changing the form of the rolled sheet obtained in step (b) or step (c) to another form in order to roll it into a sheet in the next step, and includes cases such as simply folding the rolled sheet.

[0193] Alternatively, step (c) may be performed after step (d), and this process may be repeated. Furthermore, uniaxial stretching or biaxial stretching may be performed in process (a) to (b), (c), and (d). Furthermore, the sheet strength can be adjusted by the degree of coarse crushing in process (d).

[0194] In the above steps (b), (c), or (d), the rolling ratio is preferably 10% or more, more preferably 20% or more, and also preferably in the range of 80% or less, more preferably 65% ​​or less, and even more preferably 50% or less. If it is below the above range, the time required will increase with the number of rolling cycles, affecting productivity. If it is above the above range, fibrillation may proceed excessively, potentially resulting in an electrode mixture sheet with poor strength and flexibility. The rolling ratio, as used here, refers to the percentage reduction in thickness after rolling compared to the thickness of the sample before rolling. The sample before rolling may be a bulk raw material composition or a sheet raw material composition. The thickness of the sample refers to the thickness in the direction in which the load is applied during rolling. Steps (c) to (d) described above are preferably carried out at 30°C or higher, and more preferably at 60°C or higher. Furthermore, it is preferable to carry them out at 150°C or lower.

[0195] The above electrode mixture sheet can be used as an electrode mixture sheet for secondary batteries. It can be used as either the negative electrode or the positive electrode. In particular, the above electrode mixture sheet is suitable for lithium-ion secondary batteries.

[0196] This disclosure also provides an electrode comprising the PTFE powder or electrode binder described herein, an electrode active material, and a current collector. The electrode of this disclosure is a sustainable product and can suppress gas generation inside the battery cell and degradation of battery characteristics (e.g., decrease in capacity during high-temperature storage). It also has excellent strength.

[0197] The electrode of this disclosure may include the electrode mixture (preferably an electrode mixture sheet) and a current collector as described above.

[0198] The electrode of this disclosure may be a positive electrode or a negative electrode.

[0199] The positive electrode described above preferably consists of a current collector and an electrode mixture sheet containing the positive electrode active material. Suitable materials for the positive electrode current collector include metals such as aluminum, titanium, tantalum, stainless steel, and nickel, or their alloys; and carbon materials such as carbon cloth and carbon paper. Among these, metal materials, particularly aluminum or its alloys, are preferred.

[0200] Examples of current collector shapes include metal foil, metal cylinders, metal coils, metal plates, expanded metal, punched metal, and foamed metal in the case of metal materials, and carbon plates, carbon thin films, and carbon cylinders in the case of carbon materials. Of these, metal foil is preferred. The metal foil may be formed into a mesh shape as appropriate. The thickness of the metal foil is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, and more preferably 50 μm or less. If the metal foil is thinner than this range, it may lack the necessary strength as a current collector. Conversely, if the metal foil is thicker than this range, its handling may be impaired.

[0201] Furthermore, it is preferable that a conductive additive is applied to the surface of the current collector, from the viewpoint of reducing the electrical contact resistance between the current collector and the positive electrode active material layer. Examples of conductive additives include carbon and precious metals such as gold, platinum, and silver.

[0202] The ratio of the thickness of the current collector to the thickness of the positive electrode mixture is not particularly limited, but the value of (thickness of one side of the positive electrode mixture immediately before electrolyte injection) / (thickness of the current collector) is preferably 20 or less, more preferably 15 or less, most preferably 10 or less, and also preferably 0.5 or more, more preferably 0.8 or more, most preferably 1 or more. If it exceeds this range, the current collector may generate heat due to Joule heating during high current density charging and discharging. If it falls below this range, the volume ratio of the current collector to the positive electrode active material increases, which may reduce the battery capacity.

[0203] The positive electrode can be manufactured by conventional methods. For example, one method involves laminating the electrode mixture sheet and the current collector with an adhesive in between, and then vacuum drying.

[0204] The density of the positive electrode mixture sheet is preferably 3.00 g / cm³. 3 More preferably, 3.10 g / cm³ 3 More preferably 3.20 g / cm³ 3 The above is true, and preferably 3.80 g / cm³. 3 The following, more preferably, is 3.75 g / cm³. 3 More preferably, 3.70 g / cm³ 3 The range is as follows. If the range is exceeded, the penetration of the electrolyte near the current collector / active material interface decreases, which can reduce charge / discharge characteristics, especially at high current densities, and may prevent high output from being obtained. Conversely, if the range is below this, the conductivity between the active materials decreases, increasing battery resistance and potentially preventing high output from being obtained.

[0205] From the viewpoint of increasing high output and stability at high temperatures, it is preferable that the area of ​​the positive electrode mixture sheet be large relative to the outer surface area of ​​the battery casing. Specifically, it is preferable that the total area of ​​the positive electrode mixture be 15 times or more the surface area of ​​the secondary battery casing, and more preferably 40 times or more. The outer surface area of ​​the battery casing refers to the total area calculated from the length, width, and thickness of the case portion filled with the power generation elements, excluding the terminal protrusions, in the case of a bottomed rectangular shape. In the case of a bottomed cylindrical shape, it is the geometric surface area approximating the case portion filled with the power generation elements, excluding the terminal protrusions, as a cylinder. The total area of ​​the positive electrode mixture refers to the geometric surface area of ​​the positive electrode mixture layer facing the mixture layer containing the negative electrode active material, and in a structure in which positive electrode mixture layers are formed on both sides via a current collector foil, it refers to the sum of the areas calculated separately for each surface.

[0206] The thickness of the positive electrode is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the composite layer, after subtracting the thickness of the metal foil of the current collector, is preferably 10 μm or more, more preferably 20 μm or more, and preferably 500 μm or less, and more preferably 450 μm or less, as a lower limit for one side of the current collector.

[0207] Furthermore, a positive electrode with a different composition attached to its surface may also be used. Examples of surface-attached substances include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0208] The negative electrode is preferably composed of a current collector and an electrode mixture sheet containing the negative electrode active material. Suitable materials for the negative electrode current collector include metals such as copper, nickel, titanium, tantalum, and stainless steel, or their alloys; and carbon materials such as carbon cloth and carbon paper. Among these, metals, particularly copper, nickel, or their alloys, are preferred.

[0209] Examples of current collector shapes include metal foil, metal cylinders, metal coils, metal plates, expanded metal, punched metal, and foamed metal in the case of metal materials, and carbon plates, carbon thin films, and carbon cylinders in the case of carbon materials. Of these, metal foil is preferred. The metal foil may be formed into a mesh shape as appropriate. The thickness of the metal foil is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, and more preferably 50 μm or less. If the metal foil is thinner than this range, it may lack the necessary strength as a current collector. Conversely, if the metal foil is thicker than this range, its handling may be impaired.

[0210] The negative electrode can be manufactured by conventional methods. For example, one method involves laminating the electrode mixture sheet and the current collector with an adhesive in between, and then vacuum drying.

[0211] The density of the negative electrode mixture is preferably 1.3 g / cm³. 3 More preferably 1.4 g / cm³ 3 More preferably 1.5 g / cm³ 3 The above is true, and preferably 2.0 g / cm³.3 More preferably, 1.9 g / cm³ 3 More preferably, 1.8 g / cm³ 3 The range is as follows. If the range is exceeded, the penetration of the electrolyte near the current collector / active material interface decreases, which can reduce charge / discharge characteristics, especially at high current densities, and may prevent high output from being obtained. Conversely, if the range is below this, the conductivity between the active materials decreases, increasing battery resistance and potentially preventing high output from being obtained.

[0212] The thickness of the negative electrode is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the composite layer, after subtracting the thickness of the metal foil of the current collector, is preferably 10 μm or more, more preferably 20 μm or more, and preferably 500 μm or less, and more preferably 450 μm or less, as a lower limit for one side of the current collector.

[0213] This disclosure also provides a secondary battery comprising the electrodes of this disclosure as described above.

[0214] The secondary battery of this disclosure may be a secondary battery that uses an electrolyte, or it may be a solid-state secondary battery.

[0215] The secondary battery using the above-mentioned electrolyte can use the same electrolyte, separator, etc. as those used in known secondary batteries. These will be described in detail below.

[0216] A non-aqueous electrolyte is preferably used as the electrolyte. As the non-aqueous electrolyte, a known electrolyte salt dissolved in a known organic solvent for dissolving electrolyte salts can be used.

[0217] The organic solvent for dissolving the electrolyte salt is not particularly limited, but one or more of the following can be used: known hydrocarbon solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and fluorinated solvents such as fluoroethylene carbonate, fluoroether, and fluorinated carbonate.

[0218] Examples of electrolyte salts include LiClO4, LiAsF6, LiBF4, LiPF6, LiN(SO2CF3)2, and LiN(SO2C2F5)2. LiPF6, LiBF4, LiN(SO2CF3)2, LiN(SO2C2F5)2, or combinations thereof are particularly preferred due to their good cycling properties.

[0219] The concentration of the electrolyte salt is preferably 0.8 mol / liter or higher, and more preferably 1.0 mol / liter or higher. The upper limit depends on the organic solvent used to dissolve the electrolyte salt, but is usually 1.5 mol / liter.

[0220] A secondary battery using the above-mentioned electrolyte is preferably further equipped with a separator. The material and shape of the separator are not particularly limited as long as they are stable in the electrolyte and have excellent liquid retention properties, and known materials can be used. In particular, it is preferable to use a porous sheet or nonwoven fabric made of a material that is stable in the electrolyte, such as resin, glass fiber, or inorganic material, and has excellent liquid retention properties.

[0221] As materials for the resin and glass fiber separator, for example, polyolefins such as polyethylene and polypropylene, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, and glass filters can be used. These materials, such as polypropylene / polyethylene two-layer films and polypropylene / polyethylene / polypropylene three-layer films, may be used individually or in any combination and ratio of two or more. In particular, the separator is preferably a porous sheet or nonwoven fabric made from polyolefins such as polyethylene and polypropylene, as it has good electrolyte permeability and shut-off effect.

[0222] The thickness of the separator is arbitrary, but is usually 1 μm or more, preferably 5 μm or more, more preferably 8 μm or more, and usually 50 μm or less, preferably 40 μm or less, and more preferably 30 μm or less. If the separator is too thin compared to the above range, the insulating properties and mechanical strength may decrease. If it is too thick compared to the above range, not only may the battery performance such as rate characteristics decrease, but the energy density of the electrolyte battery as a whole may decrease.

[0223] Furthermore, when using porous materials such as porous sheets or nonwoven fabrics as separators, the porosity of the separator is arbitrary, but is usually 20% or more, preferably 35% or more, more preferably 45% or more, and usually 90% or less, preferably 85% or less, and more preferably 75% or less. If the porosity is too small compared to the above range, the film resistance tends to increase and the rate characteristics tend to deteriorate. Also, if it is too large compared to the above range, the mechanical strength of the separator tends to decrease and the insulating properties tend to deteriorate.

[0224] Furthermore, while the average pore size of the separator is arbitrary, it is usually 0.5 μm or less, preferably 0.2 μm or less, and usually 0.05 μm or more. If the average pore size exceeds the above range, short circuits are more likely to occur. Conversely, if it falls below the above range, the film resistance increases and the rate characteristics may deteriorate.

[0225] On the other hand, inorganic materials such as oxides of alumina and silicon dioxide, nitrides of aluminum nitride and silicon nitride, and sulfates of barium sulfate and calcium sulfate are used, and these are available in particulate or fibrous form.

[0226] In terms of form, thin films such as nonwoven fabrics, woven fabrics, and microporous films are used. In the thin film form, those with a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm are preferably used. In addition to the independent thin film forms described above, separators can be used in which a composite porous layer containing the inorganic particles is formed on the surface of the positive and / or negative electrode using a resin binder. For example, a porous layer can be formed on both sides of the positive electrode using alumina particles with a 90% particle size of less than 1 μm and a fluororesin as a binder.

[0227] The electrode mixture group may be either a laminated structure in which the positive electrode and negative electrode are separated by the separator, or a structure in which the positive electrode and negative electrode are spirally wound around the separator. The proportion of the volume of the electrode mixture group to the internal volume of the battery (hereinafter referred to as the electrode mixture group occupancy rate) is usually 40% or more, preferably 50% or more, and usually 90% or less, preferably 80% or less.

[0228] If the electrode mixture occupancy rate falls below the above range, the battery capacity will decrease. Conversely, if it exceeds the above range, the void space is small, and as the battery heats up, the components expand and the vapor pressure of the electrolyte liquid component increases, causing the internal pressure to rise. This reduces the battery's charge / discharge cycle performance and high-temperature storage capabilities, and may even cause the gas release valve, which releases internal pressure, to activate.

[0229] The current collection structure is not particularly limited, but in order to more effectively improve the high-current-density charge-discharge characteristics using the electrolyte, it is preferable to have a structure that reduces the resistance of the wiring and connection parts. When the internal resistance is reduced in this way, the effect of using the electrolyte is particularly well exhibited.

[0230] In the case of electrode mixtures having the above-described laminated structure, a structure formed by bundling the metal core portions of each electrode mixture layer and welding them to a terminal is preferably used. When the area of ​​a single electrode mixture is large, the internal resistance increases, so it is also preferable to provide multiple terminals within the electrode mixture to reduce the resistance. In the case of electrode mixtures having the above-described wound structure, the internal resistance can be lowered by providing multiple lead structures for both the positive and negative electrodes and bundling them to a terminal.

[0231] The material of the outer casing is not particularly limited as long as it is a stable material for the electrolyte used. Specifically, metals such as nickel-plated steel, stainless steel, aluminum or aluminum alloy, magnesium alloy, or laminated films of resin and aluminum foil can be used. From the viewpoint of weight reduction, aluminum or aluminum alloy metals or laminated films are preferably used.

[0232] Outer cases using metals may be sealed by welding the metals together using laser welding, resistance welding, or ultrasonic welding, or by using a crimped structure with the metals connected via a resin gasket. Outer cases using laminate film may be sealed by heat-fusing the resin layers together. To improve sealing performance, a resin different from the resin used in the laminate film may be interposed between the resin layers. In particular, when a sealed structure is formed by heat-fusing the resin layers via a current collector terminal, since it is a joint between metal and resin, a resin having polar groups or a modified resin with introduced polar groups is preferably used as the interposing resin.

[0233] The shape of the secondary battery using the above-mentioned electrolyte is arbitrary, and examples include cylindrical, prismatic, laminated, coin-type, and large-sized shapes. The shape and configuration of the positive electrode, negative electrode, and separator can be changed and used according to the shape of each battery.

[0234] The above-mentioned solid secondary battery is preferably an all-solid-state secondary battery. The above-mentioned solid secondary battery is preferably a lithium-ion battery, and also preferably a sulfide-based all-solid-state secondary battery. The above-mentioned solid secondary battery preferably includes a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode.

[0235] The solid electrolyte used in the solid secondary battery binder may be a sulfide-based solid electrolyte or an oxide-based solid electrolyte. In particular, when using a sulfide-based solid electrolyte, there is an advantage of flexibility.

[0236] The above-mentioned sulfide-based solid electrolyte is not particularly limited, and may be Li2S-P2S5, Li2S-P2S3, Li2S-P2S3-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, LiI-Li2S-SiS2-P2S5, Li2S-SiS2-Li4SiO4, Li2S-SiS2-Li3PO4, Li3PS4-Li4GeS4, Li 3.4 P 0.6 Si 0.4 S4, Li 3.25 P 0.25 Ge 0.76 S4, Li 4-x Ge 1-x P x S4(X = 0.6 to 0.8), Li 4+y Ge 1-y Ga y S4(y = 0.2 to 0.3), LiPSCl, LiCl, Li 7-x-2y PS 6-x-y Cl x (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5), etc., or a mixture of two or more thereof can be used.

[0237] The above sulfide-based solid electrolyte preferably contains lithium. A lithium-containing sulfide-based solid electrolyte is used in solid-state batteries that use lithium ions as carriers and is particularly preferred in that it is an electrochemical device with high energy density.

[0238] The oxide-based solid electrolyte described above is preferably a compound that contains oxygen atoms (O), has the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and is also an electronically insulating compound.

[0239] Specific examples of compounds include, for example, Li xa La ya TiO3 [xa=0.3~0.7, ya=0.3~0.7] (LLT), Li xb La yb Zr zb M bb mb O nb (M bb (The elements are Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, and xb satisfies 5 ≤ ​​xb ≤ 10, yb satisfies 1 ≤ yb ≤ 4, zb satisfies 1 ≤ zb ≤ 4, mb satisfies 0 ≤ mb ≤ 2, and nb satisfies 5 ≤ ​​nb ≤ 20.) , Li xc B yc M cc zc O nc (M cc (The element is C, S, Al, Si, Ga, Ge, In, Sn, and xc satisfies 0 ≤ xc ≤ 5, yc satisfies 0 ≤ yc ≤ 1, zc satisfies 0 ≤ zc ≤ 1, and nc satisfies 0 ≤ nc ≤ 6.) Li xd (Al,Ga) yd (Ti,Ge) zd Si ad P md O nd (wherein 1≦xd≦3, 0≦yd≦2, 0≦zd≦2, 0≦ad≦2, 1≦md≦7, 3≦nd≦15), Li (3-2xe) M ee xe D ee O(xe represents a number between 0 and 0.1, M eeD represents a divalent metal atom. ee ) represents a halogen atom or a combination of two or more halogen atoms. ), Li xf Si yf O zf (1≦xf≦5, 0 <yf≦3、1≦zf≦10)、Li xg S yg O zg (1 ≤ xg ≤ 3, 0 <yg≦2、1≦zg≦10)、Li3BO3-Li2SO4、Li2O-B2O3-P2O5、Li2O-SiO2、Li6BaLa2Ta2O 12 Li3PO (4-3 / 2w) N w (where w < 1), Li has a LISICON (Lithium superionic conductor) type crystal structure. 3.5 Zn 0.25 La, which has a perovskite crystal structure, is GeO4. 0.51 Li 0.34 TiO 2.94 La 0.55 Li 0.35 LiTi2P3O has a TiO3, NASICON (Natrium superionic conductor) type crystal structure. 12 Li 1+xh+yh (Al,Ga) xh (Ti,Ge) 2-xh Si yh P 3-yh O 12 (where 0≦xh≦1, 0≦yh≦1), Li7La3Zr2O has a garnet-type crystal structure. 12 Examples include (LLZ). Furthermore, ceramic materials in which elemental substitutions have been performed on LLZ are also known. For example, LLZ-based ceramic materials in which at least one element, Mg (magnesium) and A (A being at least one element selected from the group consisting of Ca (calcium), Sr (strontium), and Ba (barium)), has been substituted onto LLZ. Phosphorus compounds containing Li, P, and O are also desirable. Examples include lithium phosphate (Li3PO4), LiPON (in which some of the oxygen in lithium phosphate is substituted with nitrogen), and LiPOD. 1 (D 1Examples include at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc. Also, LiA 1 ON(A 1 (At least one selected from Si, B, Ge, Al, C, Ga, etc.) can also be preferably used. Specific examples include Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2 and Li2O-Al2O3-SiO2-P2O5-TiO2.

[0240] The above oxide-based solid electrolyte is preferably lithium-containing. A lithium-containing oxide-based solid electrolyte is used in solid-state batteries that use lithium ions as carriers and is particularly preferred in that it is an electrochemical device with high energy density.

[0241] The above oxide-based solid electrolyte is preferably an oxide having a crystalline structure. Oxides having a crystalline structure are particularly preferred in terms of good Li ion conductivity. Examples of oxides having a crystalline structure include perovskite type (La 0.51 Li 0.34 TiO 2.94 etc.), NASICON type (Li 1.3 Al 0.3 Ti 1.7 (PO4)3, garnet type (Li7La3Zr2O 12 Examples include (LLZ, etc.). Among these, the NASICON type is preferred.

[0242] The volume-average particle size of oxide-based solid electrolytes is not particularly limited, but is preferably 0.01 μm or larger, and more preferably 0.03 μm or larger. The upper limit is preferably 100 μm or smaller, and more preferably 50 μm or smaller. The average particle size of oxide-based solid electrolyte particles is measured using the following procedure: A 1% by mass dispersion of oxide-based solid electrolyte particles is prepared in a 20 ml sample bottle using water (or heptane if the substance is unstable in water). The diluted dispersion sample is irradiated with 1 kHz ultrasound for 10 minutes and used immediately afterward. Using this dispersion sample, data is acquired 50 times using a laser diffraction / scattering particle size distribution analyzer LA-920 (manufactured by HORIBA) at a temperature of 25°C using a quartz cell to obtain the volume-average particle size. For other detailed conditions, refer to JIS Z 8828:2013 "Particle Size Analysis - Dynamic Light Scattering Method" as needed. Five samples are prepared for each level, and their average value is adopted.

[0243] The above-mentioned solid-state secondary battery may include a separator between the positive electrode and the negative electrode. Examples of the separator include porous membranes such as polyethylene and polypropylene; and nonwoven fabrics such as resin nonwoven fabrics such as polypropylene and glass fiber nonwoven fabrics.

[0244] The above-mentioned solid-state secondary battery may further include a battery case. The shape of the battery case is not particularly limited as long as it can accommodate the positive electrode, negative electrode, solid electrolyte layer, etc., as described above, but specific examples include cylindrical, prismatic, coin-shaped, laminated, etc.

[0245] The above-mentioned solid-state secondary battery can be manufactured, for example, by sequentially stacking a positive electrode, a solid electrolyte layer sheet, and a negative electrode, and then pressing them together. [Examples]

[0246] The present disclosure will now be further described with reference to examples, but the present disclosure is not limited to these examples.

[0247] Various physical properties were measured using the following method.

[0248] Average primary particle size A PTFE aqueous dispersion is diluted with water until the solid content concentration reaches 0.15% by mass. A calibration curve is created by measuring the transmittance of 550 nm projected light per unit length of the resulting diluted latex and the number-referenced length-average particle diameter determined by measuring the direction using transmission electron microscopy. Using this calibration curve, the number-average particle diameter is determined from the measured transmittance of 550 nm projected light for each sample and is defined as the average primary particle diameter.

[0249] Average aspect ratio A PTFE aqueous dispersion diluted to a solid content concentration of approximately 1% by mass was observed using a scanning electron microscope (SEM). Image processing was performed on more than 200 randomly selected particles, and the ratio of their major axis to minor axis was used to determine the result.

[0250] apparent density Measurements were taken in accordance with JIS K6892.

[0251] Average secondary particle size Measurements were taken in accordance with JIS K6891.

[0252] Standard specific gravity (SSG) Samples were prepared in accordance with ASTM D 4895 and measured using the water displacement method in accordance with ASTM D 792.

[0253] PMVE content Dissolve the PTFE powder at 370°C, 19 1F-NMR measurements were performed, and the signal originating from the obtained functional group was calculated based on the following formula. PMVE content (mass%)=(664B / (300A+364B))×100 (A: The sum of the CF2 signal appearing around -120 ppm and the CF signal appearing around -136 ppm; B: The sum of the CF3 signal originating from PMVE appearing around -54 ppm) The chemical shift values ​​used were those obtained with the peak top of the CF2 signal derived from the polymer backbone set to -120 ppm.

[0254] CTFE content A thin film disc was created by press-molding PTFE powder, and the infrared absorbance of the thin film disc was measured using FT-IR, resulting in a value of 957 cm⁻¹. -1 Absorbance / 2360cm² -1 It was calculated by multiplying the ratio of absorbances by 0.58.

[0255] HFP content A thin film disc was created by press-molding PTFE powder, and the infrared absorbance of the thin film disc was measured using FT-IR, resulting in a value of 982 cm². -1 Absorbance at 935 cm² -1 It was calculated by multiplying the ratio of absorbances in the given location by 0.3.

[0256] VDF content PTFE powder 19 F-NMR measurements were performed. Furthermore, thin film discs were created by press-molding the PTFE powder, and the infrared absorbance measured by FT-IR was found to be 1429 cm⁻¹. -1 / 2360cm -1 The ratio of the absorbances was determined. 19 A calibration curve was created from the F-NMR measurements and the absorbance ratios mentioned above. The VDF content was calculated from this calibration curve.

[0257] Fluorine-containing compound content (1) Weigh 1 g of PTFE powder each, add 10 g (12.6 ml) of methanol, perform ultrasonic treatment for 60 minutes to obtain an extract. The obtained extract was measured by LC / MS / MS. For the fluorine-containing compounds in the extract, measurement was carried out using a liquid chromatograph mass spectrometer (Waters, LC-MS ACQUITY UPLC / TQD). The measurement equipment configuration and LC-MS measurement conditions are shown in Table 1. An aqueous solution of a fluorine-containing compound with a known concentration was used to prepare aqueous solutions with a content of 5 levels or more, and LC / MS analysis was performed on each aqueous solution with a different content. The relationship between the content and the area of the peak was plotted to draw a calibration curve. Using the above calibration curve, the area of the LC / MS chromatogram of the fluorine-containing compounds in the extract was converted to the content of the fluorine-containing compounds. The detection limit in this measurement method is 10 mass ppb.

[0258]

Table 1

[0259] Fluorine-containing compound content (2) The content of the fluorine-containing compounds contained in the PTFE powder was determined as the content of the fluorine-containing compounds extracted from the powder.

[0260] <Extraction of fluorine-containing compounds from PTFE powder> Add 10 g (12.6 mL) of methanol to 1 g of PTFE powder, and perform ultrasonic treatment at 60 °C for 2 hours. After standing at room temperature, the solid content was removed to obtain an extract.

[0261] <Measurement of perfluoroether carboxylic acids A and C> 1. Calibration curve of perfluoroether carboxylic acids A and C Five levels of methanol standard solutions of perfluoroether carboxylic acids A and C with known concentrations were prepared and measured using a liquid chromatograph mass spectrometer (Agilent, Ultivo triple quadrupole LC-MS). In each concentration range, a calibration curve was created using linear approximation from the methanol standard solution concentration and the integral value of the peak.

[0262] Measurement equipment configuration and LC-MS measurement conditions [Table 2]

[0263] MRM measurement parameters [Table 3]

[0264] 2. Content of perfluoroether carboxylic acids A and C in PTFE powder Using a liquid chromatograph-mass spectrometer, the content of perfluoroether carboxylic acids A and C in the extract was measured from a calibration curve. The content of perfluoroether carboxylic acid A in the PTFE powder was determined using the following relational equation (1). Y A =X A ×12.6 (1) Y A : Content of perfluoroether carboxylic acid A contained in the powder (mass ppb) X A : Perfluorocarboxylic acid A content in the extract (ng / mL) The content of perfluoroether carboxylic acid C in the PTFE powder was determined using the following relational equation (2). Y C =X C ×12.6 (2) Y C : Content of perfluoroether carboxylic acid C contained in the powder (mass ppb) X C : Perfluorocarboxylic acid C content in the extract (ng / mL) The limit of quantification for the content of perfluoroether carboxylic acids A-C in PTFE powder is 1 ppb by mass.

[0265] moisture content The mass of approximately 20g of PTFE powder was measured before and after heating at 150°C for 2 hours, and the mass was calculated according to the following formula. Three samples were taken, and the calculation was performed for each sample. The average value was then calculated and adopted. Moisture content (mass %) = [(Mass of PTFE powder before heating (g)) - (Mass of PTFE powder after heating (g))] / (Mass of PTFE powder before heating (g)) × 100

[0266] Stretchability The bead obtained by the paste extrusion described above was dried at 230°C for 30 minutes to remove the lubricant. After drying, the bead was cut to an appropriate length and placed in a furnace heated to 300°C. Inside the furnace, it was stretched at a stretching speed of 100% / second until it reached 25 times the length of the bead before the stretching test. Beads that did not break during stretching were evaluated as stretchable, and those that broke were evaluated as not stretchable.

[0267] Battery evaluation <Preparation of positive electrode mixture sheet> Li(Ni) is used as the positive electrode active material. 0.6 Mn 0.2 Co 0.2 O2 (NMC622) and carbon black as a conductive additive were weighed and stirred at 30 rpm for 300 seconds using a pressurized kneader to obtain a mixture. Subsequently, PTFE powder was added as a binder, and the mixture was stirred at 50 rpm for 300 seconds to obtain the mixture. The mass ratio of positive electrode active material:binder:conductive additive was set to 95:2:3. The resulting mixture was formed into a bulk and then rolled into a sheet. Subsequently, the rolled sheet obtained earlier was roughly crushed by folding it in half, then reshaped into a bulk form. This process of rolling it into a sheet on a flat plate using metal rolls to promote fibrillation was repeated four times. After that, further rolling was performed to obtain a cathode mixture sheet with a thickness of approximately 500 μm. Furthermore, the cathode mixture sheet was cut into 5 cm x 5 cm pieces and rolled in a roll press machine. To further promote fibrillation, a load of 2 kN was repeatedly applied to adjust the thickness. The gap was adjusted so that the final cathode mixture layer thickness was 90 μm and the density was 3.30 g / cc.

[0268] <Strength measurement of positive electrode mixture sheet> The above positive electrode mixture sheet was cut to create 4mm wide strip-shaped test pieces. Measurements were taken using a tensile testing machine (Shimadzu AGS-100NX) under a stress of 100mm / min. The chuck distance was 30mm. Displacement was applied until fracture, and the maximum stress measured was defined as the strength of each sample. Example 1 was set as 100 for comparison.

[0269] <Fabrication of the positive electrode> The above positive electrode mixture sheet was bonded to a 20 μm aluminum foil as follows. The adhesive used was a slurry prepared by dissolving polyvinide fluoride (PVDF) in N-methylpyrrolidone (NMP) and dispersing carbon nanotubes (CNTs). The aforementioned adhesive was applied to aluminum foil and dried on a hot plate at 120°C for 15 minutes to form a current collector with an adhesive layer. Subsequently, the positive electrode mixture sheet was placed on the current collector with an adhesive layer, and the positive electrode mixture sheet and current collector were bonded together using a roll press heated to 180°C. The sheet was then cut to the desired size, tabs were attached, and it was made into a positive electrode.

[0270] <Fabrication of the negative electrode> 98 parts by mass of carbonaceous material (graphite) was mixed with 1 part by mass of aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose 1% by mass) and 1 part by mass of aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber 50% by mass) as a thickener and binder, respectively, and mixed in a disperser to form a slurry. The resulting slurry was applied to a 10 μm thick copper foil, dried, rolled in a press, cut to the desired size, and tabbed to form the negative electrode.

[0271] <Preparation of electrolyte solution> As an organic solvent, a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC = 30:70 (volume ratio)) was weighed into a sample bottle, and fluoroethylene carbonate (FEC) and vinylene carbonate (VC) were dissolved in it at a concentration of 1% by mass each to prepare a mixture. A non-aqueous electrolyte was obtained by mixing LiPF6 salt into this mixture at 23°C so that the concentration in the electrolyte was 1.0 mol / L.

[0272] <Fabrication of aluminum laminate cells> The positive electrode described above was placed opposite the negative electrode via a 20 μm thick microporous polyethylene film (separator), the non-aqueous electrolyte obtained above was injected, and after the non-aqueous electrolyte had sufficiently permeated the separator, etc., it was sealed, pre-charged and aged to produce a lithium-ion secondary battery.

[0273] <Evaluation of storage characteristics (remaining volume percentage, gas generation amount)> The lithium-ion secondary battery manufactured as described above was charged to 4.3V at 25°C using a constant current-constant voltage charge (hereinafter referred to as CC / CV charge) with a current equivalent to 0.5C (0.1C cutoff). Then, it was discharged to 3V with a constant current of 0.5C. This was considered one cycle, and the initial discharge capacity was determined from the discharge capacity of the third cycle. After the initial resistance evaluation was completed, the batteries were recharged to 4.3V at 25°C using CC / CV charging (0.1C cut-off), and the battery volume was determined. After determining the battery volume, the batteries were stored at high temperature at 60°C for 30 days. After the high-temperature storage period, the batteries were cooled sufficiently, and the battery volume was determined at 25°C. The amount of gas generated was calculated from the difference in battery volume before and after the storage test. The amount of gas generated in Example 1 was set to 100, and the amounts of gas generated were compared. After determining the amount of gas, the battery was discharged to 3V at 0.5C at 25°C, and the remaining capacity was determined. The ratio of the remaining capacity after high-temperature storage to the initial discharge capacity was determined and defined as the remaining capacity percentage (%). (Residual capacity) / (Initial discharge capacity)×100=Remaining capacity rate (%)

[0274] The following fluorine-containing compounds with a molecular weight of 1000 or less were prepared. Ammonium perfluoroether carboxylate A ammonium salt: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Ammonium perfluoro(2-methyl-3-oxahexanoate), structural formula: CF3CF2CF2OCF(CF3)COONH4 Ammonium perfluoro-3,6-dioxaoctanoate, structural formula: CF3CF2OCF2CF2OCF2COONH4 Ammonium 2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(trifluoromethoxy)propoxy]-propionate, structural formula: CF3OCF(CF3)CF2OCF(CF3)COONH4

[0275] The following hydrophilic monomers were prepared. Hydrophilic monomer D: Ammonium 2,3,3,3-tetrafluoro-2-[(1,1,2-trifluoro-2-propenyl)oxy]-Propanoate, structural formula: CH2=CFCF2OCF(CF3)COONH4

[0276] Manufacturing Example 1 In a 6-liter stainless steel autoclave equipped with stainless steel stirring blades and a temperature control jacket, 3480g of deionized water, 100g of paraffin wax, 15.75g of ammonium salt of perfluoroether carboxylic acid A, and 35mg of hydrophilic monomer D were charged. The autoclave was heated to 70°C while the inside was purged with nitrogen gas to remove oxygen. A TFE was injected under pressure to set the system pressure to 0.78 MPaG, and the system temperature was maintained at 70°C while stirring. Next, an aqueous solution of 14.0mg of ammonium persulfate dissolved in 20g of water was injected under pressure using the TFE to start the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but additional TFE was added to maintain the system temperature at 70°C and the system pressure at 0.78 MPaG. When 433g of TFE had been consumed since the start of polymerization, an aqueous solution of 17.0mg of hydroquinone dissolved in 20g of water was injected under pressure through the TFE as a radical scavenger. Polymerization continued thereafter, and when the amount of TFE polymerized reached 1273g from the start of polymerization, stirring and the supply of TFE were stopped, and the gas in the system was immediately released to restore atmospheric pressure, thus terminating the polymerization reaction. The aqueous dispersion was taken out, cooled, and the paraffin wax was separated to obtain aqueous PTFE dispersion A. The average primary particle size of the obtained aqueous PTFE dispersion A was 295nm, and the solid content concentration was 26.5% by mass.

[0277] Example 1 The aqueous PTFE dispersion A obtained in Production Example 1 was diluted to a solid content concentration of 13% by mass, and the PTFE was allowed to coagulate while stirring in a container. The dispersion was then filtered off with water to obtain a wet powder. The moisture content of the wet powder was approximately 40% by mass. The obtained PTFE-moistened powder was placed in a stainless steel mesh tray (distribution amount: 2.0 g / cm²). 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 180°C. After 5 hours, the mesh tray was removed, air-cooled, and then PTFE powder was obtained. The SSG value of the obtained PTFE powder was 2.158.

[0278] Comparative Example 1 PTFE powder was obtained in the same manner as in Example 1, except that the stainless steel mesh tray was replaced with a stainless steel flat tray (a tray with no ventilation on the bottom and sides; the same applies hereinafter).

[0279] Comparative Example 2 PTFE powder was obtained in the same manner as in Comparative Example 1, except that the heat treatment time was changed from 5 hours to 20 hours.

[0280] Manufacturing Example 2 In a 6-liter stainless steel autoclave equipped with stainless steel stirring blades and a temperature control jacket, 3600g of deionized water, 180g of paraffin wax, 5.4g of ammonium perfluoroether carboxylic acid B, 0.108g of succinic acid, and 0.0252g of oxalic acid were charged. The polymerization vessel was heated to 70°C while the inside was replaced with nitrogen gas to remove oxygen. After maintaining the temperature inside the vessel at 70°C while stirring, TFE gas was introduced to a pressure of 2.7 MPaG. While stirring the contents, deionized water containing 3.5 mg of potassium permanganate was continuously added at a constant rate, and TFE was continuously supplied so that the pressure in the polymerization tank remained constant at 2.7 MPaG. When the TFE consumption reached 184 g, 3.8 g of ammonium salt of perfluoroether carboxylic acid B was added, and when the TFE consumption reached 900 g, the entire amount of deionized water containing the above 3.5 mg of potassium permanganate was added. When the TFE consumption reached 1543 g, stirring and TFE supply were stopped, the TFE in the polymerization tank was purged, and the polymerization reaction was terminated. The aqueous dispersion was removed, cooled, and the paraffin wax was separated to obtain aqueous PTFE dispersion B. The average primary particle size of the obtained aqueous PTFE dispersion B was 310 nm, and the solid content concentration was 30.6 mass%.

[0281] Example 2 The aqueous PTFE dispersion B obtained in Production Example 2 was diluted to a solid content concentration of 13% by mass. Nitric acid was added as a coagulant while stirring in a container to solidify the PTFE, and then the dispersion was filtered off with water to obtain a wet powder. The moisture content of the wet powder was approximately 40% by mass. The obtained PTFE-moistened powder was placed in a stainless steel mesh tray (distribution amount: 2.0 g / cm²). 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 180°C. After 5 hours, the mesh tray was removed, air-cooled, and then PTFE powder was obtained. The SSG value of the obtained PTFE powder was 2.153.

[0282] Comparative Example 3 PTFE powder was obtained in the same manner as in Example 2, except that the stainless steel mesh tray was replaced with a stainless steel flat tray, and the heat treatment was changed from 180°C for 5 hours to 210°C for 18 hours.

[0283] Manufacturing Example 3 In a 6-liter stainless steel autoclave equipped with stainless steel stirring blades and a temperature control jacket, 3560 g of deionized water, 104 g of paraffin wax, 5.4 g of ammonium salt of perfluoroether carboxylic acid C, and 35 mg of hydrophilic monomer D were charged. The autoclave was heated to 70°C while the inside was purged with nitrogen gas to remove oxygen. TFE was injected under pressure to set the system pressure to 0.60 MPaG, and the system temperature was maintained at 70°C while stirring. Next, 0.60 g of perfluoro(methyl vinyl ether) (PMVE) was injected under pressure using TFE. Subsequently, an aqueous solution of 15 mg of ammonium persulfate dissolved in 20 g of deionized water was injected under pressure using TFE, setting the system pressure to 0.78 MPaG, and the polymerization reaction was started. As the polymerization reaction progressed, the system pressure decreased, but TFE was added to maintain the system temperature at 70°C and the system pressure at 0.78 MPaG. When 429 g of TFE had been consumed since the start of polymerization, an aqueous solution of 14 mg of hydroquinone dissolved in 20 g of deionized water was injected under pressure through the TFE as a radical scavenger. Polymerization continued thereafter, and when the amount of TFE polymerized reached 1225 g from the start of polymerization, stirring and the supply of TFE were stopped, and the gas in the system was immediately released to restore atmospheric pressure, thus terminating the polymerization reaction. The aqueous dispersion was taken out, cooled, and the paraffin wax was separated to obtain aqueous PTFE dispersion C. The average primary particle size of the obtained aqueous PTFE dispersion C was 234 nm, and the solid content concentration was 25.4% by mass.

[0284] Example 3 The aqueous PTFE dispersion C obtained in Production Example 3 was diluted to a solid content concentration of 13% by mass. Nitric acid was added as a coagulant while stirring in a container to solidify the PTFE, and then the dispersion was filtered off with water to obtain a wet powder. The moisture content of the wet powder was approximately 40% by mass. The obtained PTFE-moistened powder was placed in a stainless steel mesh tray (distribution amount: 2.0 g / cm²). 2The mesh tray was heat-treated in a hot air circulating electric furnace at 180°C. After 20 hours, the mesh tray was removed, air-cooled, and then PTFE powder was obtained. The obtained PTFE powder had a PMVE content of 0.046% by mass and an SSG of 2.145.

[0285] Comparative Example 4 PTFE powder was obtained in the same manner as in Example 3, except that the stainless steel mesh tray was replaced with a stainless steel flat tray, and the heat treatment was changed from 180°C for 20 hours to 210°C for 18 hours.

[0286] The physical properties of each PTFE powder obtained above were measured using the method described above. Furthermore, a positive electrode mixture sheet, an electrode, and a lithium-ion secondary battery were fabricated using each PTFE powder obtained above, and evaluated using the method described above. The results are shown in Tables 4 and 5.

[0287] [Table 4]

[0288] [Table 5]

[0289] In the PTFE powders obtained in Examples 1 to 3, no fluorine-containing compound represented by the following formula was detected, or its content was 10 ppb by mass or less. F(CF2)7COOH, F(CF2)5COOH, H(CF2)6COOH, H(CF2)7COOH, CF3O(CF2)3OCHFCF2COOH, C3F7OCF(CF3)CF2OCF(CF3)COOH, CF3CF2CF2OCF(CF3)COOH (perfluoroether carboxylic acid A), CF3CF2OCF2CF2OCF2COOH (perfluoroether carboxylic acid B), C2F5OCF(CF3)CF2OCF(CF3)COOH, CF3OCF(CF3)CF2OCF(CF3)COOH (perfluoroether carboxylic acid C), CF2ClCF2CF2OCF(CF3)CF2OCF2COOH, CF2ClCF2CF2OCF2CF(CF3)OCF2COOH, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOH, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOH, and, [ka] (In the equation, M is H.)

[0290] Manufacturing Example 4 3600g of deionized water, 180g of paraffin wax, 5.4g of ammonium perfluoroether carboxylic acid C, and 26.5mg of oxalic acid were added to a 6L stainless steel reactor equipped with a stirrer. The contents of the reactor were then heated to 70°C while being aspirated, and simultaneously purged with tetrafluoroethylene (TFE) to remove oxygen from the reactor, and the contents were stirred. 2.60g of chlorotrifluoroethylene (CTFE) was injected into the reactor under pressure using TFE, and TFE was continued to be added until the pressure reached 2.70 MPaG. As an initiator, an aqueous solution of potassium permanganate, prepared by dissolving 3.4mg of potassium permanganate in deionized water, was continuously added to the reactor. After the injection of the initiator, a pressure drop occurred, and the start of polymerization was observed. TFE was added to the reactor to maintain a constant pressure of 2.70 MPaG. When the amount of TFE added reached 430g, the addition of the aqueous potassium permanganate solution was stopped. The reaction was terminated when the amount of TFE added reached 1660g by stopping the supply of TFE and ceasing stirring. Subsequently, the reactor was evacuated until the pressure returned to atmospheric pressure, nitrogen purging was performed, and the contents were removed from the reactor and cooled. The paraffin wax was removed to obtain an aqueous PTFE dispersion. The solid content concentration of the obtained aqueous PTFE dispersion was 31.4% by mass, and the average primary particle size was 248 nm.

[0291] Example 4 The PTFE aqueous dispersion obtained in Production Example 4 was diluted to a solid content concentration of 13% by mass, vigorously stirred in a container with a stirrer to solidify, and then filtered to obtain a wet powder. The moisture content of the wet powder was approximately 40% by mass. The obtained wet powder was placed in a stainless steel mesh tray (distribution amount: 2.0 g / cm²). 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 210°C. After 18 hours, the mesh tray was removed and air-cooled to obtain PTFE powder. Various physical properties of the obtained PTFE powder were measured. The SSG of the obtained PTFE powder was 2.150, and the CTFE content was 0.100 mass%. Furthermore, a positive electrode mixture sheet, an electrode, and a lithium-ion secondary battery were fabricated and evaluated using each of the PTFE powders obtained above by the method described above. The results are shown in Tables 6 and 7.

[0292] Manufacturing Example 5 Polymerization was carried out under the same conditions as in Preparation Example 4, except that the amount of CTFE added was changed to 1.28 g, the amount of potassium permanganate added to 3.87 mg, and the final amount of TFE was changed to 1790 g, to obtain an aqueous PTFE dispersion. The solid content concentration of the obtained aqueous PTFE dispersion was 33.0% by mass, and the average primary particle size was 263 nm.

[0293] Example 5 Using the PTFE aqueous dispersion obtained in Production Example 5, a wet powder was obtained in the same manner as in Example 4. The moisture content of the wet powder was approximately 40% by mass. The obtained wet powder was placed in a stainless steel mesh tray (distribution amount: 2.0 g / cm²). 2 PTFE powder was obtained in the same manner as in Example 4. Various physical properties of the obtained PTFE powder were measured. The SSG of the obtained PTFE powder was 2.150, and the CTFE content was 0.050 mass%. Furthermore, a positive electrode mixture sheet, an electrode, and a lithium-ion secondary battery were prepared and evaluated using each of the PTFE powders obtained above in the manner described above. The results are shown in Tables 6 and 7.

[0294] Manufacturing Example 6 In a 6-liter stainless steel autoclave equipped with stainless steel stirring blades and a temperature control jacket, 3580g of deionized water, 100g of paraffin wax, and 5.4g of ammonium salt of perfluoroether carboxylate C were charged. The autoclave was heated to 70°C while the inside was purged with nitrogen gas to remove oxygen. 0.50g of HFP was injected under pressure using a TFE, and then more TFE was injected to bring the system pressure to 0.78 MPaG. The system temperature was maintained at 70°C while stirring. Next, an aqueous solution of 15.4mg of ammonium persulfate dissolved in 20g of water was injected under pressure using a TFE to start the polymerization reaction. As the polymerization reaction progressed, the system pressure decreased, but more TFE was added to maintain the system temperature at 70°C and the system pressure at 0.78 MPaG. When 430g of TFE had been consumed since the start of polymerization, an aqueous solution of 18.0mg of hydroquinone dissolved in 20g of water was injected under pressure through the TFE as a radical scavenger. Polymerization continued thereafter, and when the amount of TFE polymerized reached 1540g from the start of polymerization, stirring and the supply of TFE were stopped, and the gas in the system was immediately released to restore atmospheric pressure, thus terminating the polymerization reaction. The aqueous dispersion was taken out, cooled, and the paraffin wax was separated to obtain an aqueous PTFE dispersion. The solid content concentration of the obtained aqueous PTFE dispersion was 29.6% by mass, and the average primary particle size was 246nm.

[0295] Example 6 The PTFE aqueous dispersion obtained in Production Example 6 was diluted to a solid concentration of 13% by mass, stirred in a container with a stirrer to solidify, and then filtered to obtain a wet powder. The moisture content of the wet powder was approximately 40% by mass. The obtained wet powder was placed in a stainless steel mesh tray (distribution amount: 2.0 g / cm²). 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 180°C. After 18 hours, the mesh tray was removed, air-cooled, and then PTFE powder was obtained. The various physical properties of the obtained PTFE powder were measured. The SSG of the obtained PTFE powder was 2.146, and the HFP content was 0.019 mass%. Furthermore, using each of the PTFE powders obtained above, positive electrode mixture sheets, electrodes, and lithium-ion secondary batteries were fabricated and evaluated using the method described above. The results are shown in Tables 6 and 7.

[0296] Manufacturing example 7 A PTFE aqueous dispersion was obtained in the same manner as in Production Example 6, except that the amount of HFP added was changed to 0.06 g. The solid content concentration of the obtained PTFE aqueous dispersion was 29.2% by mass, and the average primary particle size was 274 nm.

[0297] Example 7 Using the PTFE aqueous dispersion obtained in Production Example 7, a wet powder was obtained in the same manner as in Example 6. The moisture content of the wet powder was approximately 40% by mass. The obtained wet powder was placed in a stainless steel mesh tray (distribution amount: 2.0 g / cm²). 2 PTFE powder was obtained in the same manner as in Example 6, except that the heat treatment temperature was changed to 160°C. The various physical properties of the obtained PTFE powder were measured. The SSG of the obtained PTFE powder was 2.154, and the HFP content was 0.002% by mass. Furthermore, using each of the PTFE powders obtained above, positive electrode composite sheets, electrodes, and lithium-ion secondary batteries were fabricated and evaluated using the method described above. The results are shown in Tables 6 and 7.

[0298] Manufacturing Example 8 3600g of deionized water, 180g of paraffin wax, and 5.4g of ammonium perfluoroether carboxylic acid C were added to a 6L stainless steel reactor equipped with a stirrer. The contents of the reactor were then heated to 80°C while being aspirated, and simultaneously purged with tetrafluoroethylene (TFE) to remove oxygen from the reactor, and the contents were stirred. 3.1g of vinylidene fluoride (VDF) was injected into the reactor under pressure using TFE, and TFE was continued to be added until the pressure reached 2.70 MPaG. As an initiator, an aqueous solution of 7.2mg of ammonium persulfate (APS) dissolved in deionized water was added to the reactor. After the injection of the initiator, a decrease in pressure occurred, and the start of polymerization was observed. TFE was added to the reactor to maintain a constant pressure of 2.70 MPaG. When the amount of TFE added reached 430g, an aqueous solution of 18.2mg of hydroquinone dissolved in deionized water was added. The reaction was terminated when the amount of TFE added reached 1580g by stopping the supply of TFE and ceasing stirring. Subsequently, the reactor was evacuated until the pressure returned to atmospheric pressure, nitrogen purging was performed, and the contents were removed from the reactor and cooled. The paraffin wax was removed to obtain an aqueous PTFE dispersion. The solid content concentration of the obtained aqueous PTFE dispersion was 30.3% by mass, and the average primary particle size was 223 nm.

[0299] Example 8 The aqueous PTFE dispersion obtained in Production Example 8 was diluted to a solid content concentration of 13% by mass, vigorously stirred in a container with a stirrer to solidify, and then filtered to obtain a wet powder. The moisture content of the wet powder was approximately 40% by mass. The obtained wet powder was placed in a stainless steel mesh tray (distribution amount: 2.0 g / cm²). 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 210°C. After 18 hours, the mesh tray was removed and air-cooled to obtain PTFE powder. Various physical properties of the obtained PTFE powder were measured. The SSG of the obtained PTFE powder was 2.221, and the VDF content was 0.025 mass%. Furthermore, using each of the PTFE powders obtained above, positive electrode mixture sheets, electrodes, and lithium-ion secondary batteries were fabricated and evaluated using the method described above. The results are shown in Tables 6 and 7.

[0300] Manufacturing Example 9 3600g of deionized water, 180g of paraffin wax, 5.4g of ammonium perfluoroether carboxylic acid C, and 0.0265g of oxalic acid were added to a 6L stainless steel reactor equipped with a stirrer. The contents of the reactor were then heated to 70°C while being aspirated, and simultaneously purged with tetrafluoroethylene (TFE) to remove oxygen from the reactor, and the contents were stirred. 1.70g of vinylidene fluoride (VDF) was injected into the reactor under pressure using TFE, and TFE was continued to be added until the pressure reached 2.70 MPaG. As an initiator, an aqueous solution of potassium permanganate, prepared by dissolving 3.4mg of potassium permanganate in deionized water, was continuously added to the reactor. After the injection of the initiator, a pressure drop occurred, and the start of polymerization was observed. TFE was added to the reactor to maintain a constant pressure of 2.70 MPaG. When the amount of TFE added reached 430g, the addition of the aqueous potassium permanganate solution was stopped. The reaction was terminated when the amount of TFE added reached 1815g by stopping the supply of TFE and ceasing stirring. Subsequently, the reactor was evacuated until the pressure returned to atmospheric pressure, nitrogen purging was performed, and the contents were removed from the reactor and cooled. The paraffin wax was removed to obtain an aqueous PTFE dispersion. The solid content concentration of the obtained aqueous PTFE dispersion was 33.3% by mass, and the average primary particle size was 251 nm.

[0301] Example 9 The aqueous PTFE dispersion obtained in Production Example 9 was diluted to a solid content concentration of 13% by mass, vigorously stirred in a container with a stirrer to solidify, and then filtered to obtain a wet powder. The moisture content of the wet powder was approximately 40% by mass. The obtained wet powder was placed in a stainless steel mesh tray (distribution amount: 2.0 g / cm²). 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 210°C. After 18 hours, the mesh tray was removed and air-cooled to obtain PTFE powder. Various physical properties of the obtained PTFE powder were measured. The SSG of the obtained PTFE powder was 2.206 and the VDF content was 0.011 mass%. Furthermore, using each of the PTFE powders obtained above, positive electrode mixture sheets, electrodes, and lithium-ion secondary batteries were fabricated and evaluated using the method described above. The results are shown in Tables 6 and 7.

[0302] [Table 6]

[0303] [Table 7]

[0304] In the PTFE powders obtained in Examples 4 to 9, no fluorine-containing compound represented by the following formula was detected, or its content was less than 10 ppb by mass. F(CF2)7COOH, F(CF2)5COOH, H(CF2)6COOH, H(CF2)7COOH, CF3O(CF2)3OCHFCF2COOH, C3F7OCF(CF3)CF2OCF(CF3)COOH, CF3CF2CF2OCF(CF3)COOH (perfluoroether carboxylic acid A), CF3CF2OCF2CF2OCF2COOH (perfluoroether carboxylic acid B), C2F5OCF(CF3)CF2OCF(CF3)COOH, CF3OCF(CF3)CF2OCF(CF3)COOH (perfluoroether carboxylic acid C), CF2ClCF2CF2OCF(CF3)CF2OCF2COOH, CF2ClCF2CF2OCF2CF(CF3)OCF2COOH, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOH, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOH, and, [ka] (In the equation, M is H.)

[0305] Manufacturing Example 10 A 6-liter stainless steel autoclave equipped with stainless steel stirring blades and a temperature control jacket was charged with 3600g of deionized water, 180g of paraffin wax, and 5.4g of ammonium perfluoroether carboxylate C. The polymerization chamber was heated to 85°C while the oxygen was removed by purging the inside with nitrogen gas. After maintaining the chamber temperature at 85°C while stirring, TFE gas was introduced to achieve a pressure of 2.4 MPaG. While stirring the contents, deionized water containing 468mg of disuccinate peroxide was added, and polymerization was started. As polymerization progressed, the pressure inside the polymerization chamber decreased, but TFE was continuously supplied to maintain a constant pressure of 2.4 MPaG. When the TFE consumption reached 1580g, stirring and TFE supply were stopped, the TFE in the polymerization tank was purged, and the polymerization reaction was terminated. The aqueous dispersion was removed, cooled, and the paraffin wax was separated to obtain an aqueous PTFE dispersion. The average primary particle size of the obtained aqueous PTFE dispersion was 294nm, and the solid content concentration was 30.4% by mass.

[0306] Example 10 The aqueous PTFE dispersion obtained in Production Example 10 was diluted to a solid content concentration of 13% by mass, vigorously stirred in a container equipped with a stirrer to solidify, and then filtered to obtain a wet powder. The moisture content of the wet powder was approximately 40% by mass. The resulting moist powder is placed in a stainless steel mesh tray (distribution amount: 2.0 g / cm²). 2 The mesh tray was heat-treated in a hot air circulating electric furnace at 170°C. After 18 hours, the mesh tray was removed and air-cooled to obtain PTFE powder. Various physical properties of the obtained PTFE powder were measured. Furthermore, using the PTFE powder obtained above, a positive electrode mixture sheet, electrodes, and a lithium-ion secondary battery were fabricated and evaluated using the method described above. The results are shown in Tables 8-10.

[0307] [Table 8]

[0308] [Table 9]

[0309] [Table 10]

[0310] In the PTFE powder obtained in Example 10, no fluorine-containing compound represented by the following formula was detected, or its content was less than 10 ppb by mass or less than 1 ppb by mass. F(CF2)7COOH, F(CF2)5COOH, H(CF2)6COOH, H(CF2)7COOH, CF3O(CF2)3OCHFCF2COOH, C3F7OCF(CF3)CF2OCF(CF3)COOH, CF3CF2CF2OCF(CF3)COOH (perfluoroether carboxylic acid A), CF3CF2OCF2CF2OCF2COOH (perfluoroether carboxylic acid B), C2F5OCF(CF3)CF2OCF(CF3)COOH, CF3OCF(CF3)CF2OCF(CF3)COOH (perfluoroether carboxylic acid C), CF2ClCF2CF2OCF(CF3)CF2OCF2COOH, CF2ClCF2CF2OCF2CF(CF3)OCF2COOH, CF2ClCF(CF3)OCF(CF3)CF2OCF2COOH, CF2ClCF(CF3)OCF2CF(CF3)OCF2COOH, and, [ka] (In the equation, M is H.)

Claims

1. A polytetrafluoroethylene powder used as a binder for an electrode, the polytetrafluoroethylene powder having a moisture content of 0.010% by mass or less and a content of at least one kind selected from the group consisting of fluorine-containing compounds represented by the following formula of 25 ppb by mass or less, relative to the polytetrafluoroethylene powder: CF 3 CF 2 CF 2 OCF (CF 3 )COOM CF 3 CF 2 OCF 2 CF 2 OCF 2 COOM (In each formula, M is H, a metal atom, NR 1 4 , an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. R 1 is H or an organic group.)

2. Polytetrafluoroethylene powder as described in claim 1, wherein the content of each of the fluorine-containing compounds represented by the formula is 25 mass ppb or less relative to the polytetrafluoroethylene powder.

3. An electrode binder containing polytetrafluoroethylene powder, wherein the content of the polytetrafluoroethylene powder in the electrode binder is 95.0 mass% or more, the moisture content in the polytetrafluoroethylene powder is 0.010 mass% or less, and the content of at least one compound selected from the group consisting of fluorine-containing compounds represented by the following formula is 25 mass ppb or less. CF 3 CF 2 CF 2 OCF (CF 3 )COOM CF 3 CF 2 OCF 2 CF 2 OCF 2 COOM (In each formula, M is H, a metal atom, NR 1 4 , an imidazolium which may have a substituent, a pyridinium which may have a substituent, or a phosphonium which may have a substituent. R 1 is H or an organic group.)

4. An electrode binder as described in claim 3, wherein the content of each of the fluorine-containing compounds represented by the formula is 25 mass ppb or less relative to the polytetrafluoroethylene powder.

5. 5. The electrode binder according to claim 3, wherein the content of each of the fluorine-containing compounds represented by the formulas is less than 25 ppb by mass relative to the polytetrafluoroethylene powder.

6. 5. The electrode binder according to claim 3, wherein the polytetrafluoroethylene contains tetrafluoroethylene units and modified monomer units based on a modified monomer copolymerizable with tetrafluoroethylene.

7. 7. The electrode binder according to claim 6, wherein the modified monomer is at least one selected from the group consisting of perfluoro(methyl vinyl ether) and hexafluoropropylene.

8. 5. An electrode mixture comprising the polytetrafluoroethylene powder according to claim 1 or 2 or the electrode binder according to claim 3 or 4, and an electrode active material.

9. 5. An electrode comprising the polytetrafluoroethylene powder according to claim 1 or 2 or the electrode binder according to claim 3 or 4, an electrode active material, and a current collector.

10. A secondary battery comprising the electrode according to claim 9.